Title: Leather - From the Raw Material to the Finished Product
Author: Adcock, K. J.
Language: English
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LEATHER



_Common Commodities and Industries Series_

Each book in crown 8vo, cloth, with many illustrations, charts, etc.
=2s. 6d.= net.


   =Tea: From Grower to Consumer.= By A. Ibbetson.

   =Coffee: From Grower to Consumer.= By B. B. Keable.

   =Sugar: Cane and Beet.= By Geo. Martineau, C.B.

   =Cotton: From the Raw Material to the Finished Product.= By R.
   J. Peake.

   =Rubber: Production and Utilisation of the Raw Product.= By C.
   Beadle and H. P. Stevens, M.A., Ph.D., F.I.C.

   =Iron and Steel: Their Production and Manufacture.= By C. Hood.

   =Silk: Its Production and Manufacture.= By Luther Hooper.

   =Tobacco: From Grower to Smoker.= By A. E. Tanner.

   =Wool: From the Raw Material to the Finished Product.= By J. A.
   Hunter.

   =Coal: Its Origin, Method of Working, and Preparation for the
   Market.= By Francis H. Wilson, M. Inst. M.E.

   =Linen: From the Field to the Finished Product.= By Alfred S.
   Moore.

   =Timber: From the Forest to its Use in Commerce.= By William
   Bullock.

   =Clays and Clay Products.= By A. B. Searle.

   =Leather: From the Raw Material to the Finished Product.= By K.
   J. Adcock.

   =Oils: Animal, Vegetable, Essential, and Mineral.= By C.
   Ainsworth Mitchell, B.A., F.I.C.

   =Wheat and its Products.= By A. Millar.

   =Copper: From the Ore to the Metal.= By H. K. Picard, Assoc.
   Royal School of Mines, Mem. Inst. of Min. and Met.

   =Paper: Its History, Sources, and Production.= By H. A. Maddox.

   =Glass and Glass Manufacture.= By Percival Marson.

   =Soap: Its Composition, Manufacture, and Properties.= By
   William H. Simmons.

   =The Motor Industry.= By Horace Wyatt, B.A.

   =The Boot and Shoe Industry.= By J. S. Harding.

   =Gums and Resins.= By Ernest J. Parry.

   =Furniture.= By H. E. Binstead.

_Other Volumes in preparation._

  [Illustration: BLEACHING OIL-TANNED LEATHER BY EXPOSURE TO THE SUN

  The Rosary Leather Mills. Ashtead]



    _PITMAN'S COMMON COMMODITIES
    AND INDUSTRIES_

    LEATHER

    FROM THE RAW MATERIAL TO THE
    FINISHED PRODUCT

    BY
    K. J. ADCOCK

    LONDON
    SIR ISAAC PITMAN & SONS, LTD., 1 AMEN CORNER, E.C.4
    BATH, MELBOURNE AND NEW YORK



    PRINTED BY SIR ISAAC PITMAN
    & SONS, LTD., LONDON, BATH,
    MELBOURNE AND NEW YORK



CONTENTS


    CHAP.                                        PAGE
      I. EVOLUTION OF LEATHER MANUFACTURE           1

     II. HIDES AND SKINS                            5

    III. TANNING MATERIALS                         32

     IV. MACHINERY                                 52

      V. PREPARATION OF HIDES AND SKINS FOR
           TANNING                                 62

     VI. TANNING PROCESSES                         91

    VII. DRESSING, DYEING, AND FINISHING OF
           LEATHER                                112

         INDEX                                    159



LIST OF ILLUSTRATIONS


                                                 PAGE
    BLEACHING OIL-TANNED LEATHER      _Frontispiece_
    MECHANICAL FLAYING                             23
    PIM'S SYSTEM OF FLAYING                        24
    WARBLE FLY                                     28
    WARBLED KIP (584 HOLES)                        29
    WARBLED HIDE (MAGNIFIED)                       30
    TANNING EXTRACT PLANT                          48
    SHAVING CYLINDER                               53
    BLADED CYLINDER FOR BUFFING                    54
    BAND-KNIFE SPLITTING MACHINE                   54
    SHAVING KNIFE                                  55
    SHAVING MACHINE           _bet. pp._ 56 & 57
    SHAVING, OLD METHOD                            56
    SHAVING MACHINE, KNIFE GUARD                   59
    SHAVING MACHINE                                61
    DRUM TUMBLER                                   67
    FALLER STOCKS                                  67
    TANNER'S BEAM                                  68
    LIME YARD                                      73
    DEHAIRING KNIFE                                80
    DEHAIRING AND FLESHING MACHINE                 81
    FLESHING KNIFE                                 83
    SCUDDING KNIFE                                 86
    BARK MILL                                      93
    TAN-YARD                                       94
    ROUNDING OF HIDES                              95
    BARKOMETER                                     97
    PADDLE VAT                                    103
    PINNING SOLE BUTTS                            121
    ROLLING MACHINE                               122
    ROLLING SOLE LEATHER                          123
    FAN FOR DRYING                                124
    FAN FIXED IN CHAMBER                          125
    SUTCLIFFE SYSTEM OF DRYING                    126
    SLEEKER                                       128
    FLUFFING MACHINE                              129
    STRIKING-OUT AND SCOURING MACHINE             130
    LEATHER-STUFFING DRUM                         135
    STAKING AND GLAZING MACHINE                   143



LEATHER



CHAPTER I

EVOLUTION OF THE ART OF LEATHER MANUFACTURE


Before describing the making of leather by up-to-date methods, it may
be useful to attempt to outline the evolution of the ancient art of
tanning and dyeing skins. As everyone knows, leather is the preserved
skin of various animals, but the origin of the conversion of raw
skins into an imputrescible material will probably never be traced,
and it can only be assumed that the processes necessary to produce
leather from skins were gradually and, in most cases, accidentally
discovered. Long before the Christian era, the ancient Egyptians
had succeeded in bringing the manufacture of leather to remarkable
perfection, and, had they at their service the wonderful machinery
now available to the leather industry, it is certain that their
productions would have lost little or nothing by comparison with
modern leather. Happily, specimens of ancient Egyptian leather have
been preserved in one national museum, and, although they are said
to have been made at least 3,000 years ago, the colour and natural
strength of the leather are unimpaired.

Judging by the advanced state of the art of leather manufacture in
the early Egyptian period, it is obvious that the origin of its
manufacture must have considerably antedated that period, and,
indeed, it would be necessary to go back almost to the creation of
man to find the origin of the use of preserved animal skins for
clothing. The primitive method would naturally consist of simply
drying the skin, in which condition it would keep for many years
unless it came into contact with moisture, though its horniness
would no doubt cause the wearer much discomfort. It must not be
supposed that the wearing of dried raw skins with the hair left on
was impracticable, for even to-day some of the skins of fur-bearing
animals used for personal adornment are cured in this primitive
way, with the additional treatment with napthalene for disinfecting
purposes and keeping away injurious insects and moths, the object of
the limited amount of dressing being to preserve the natural strength
and coloration of the fur. In such a condition, however, the skins
are liable to acquire an unpleasant odour, and for hygienic reasons
it is advisable that all skins in the hair used for clothing or rugs
should be properly dressed, so that no decay sets in to loosen the
hair or fur.

Even now, the process of simply drying hides and skins to preserve
them before sending them to the tanner is largely practised,
especially in hot climates and in those countries where salt is not
readily available. This process of curing rests on the chemical
theory of dehydration, which, in a modified form, has recently been
successfully applied to some experiments in making leather.

Finding that the simple drying of skins would not properly prepare
them for clothing, primeval man would naturally look for some means
of treating them to conserve their original softness and pliability,
and the nearest substances at hand would be animal fats and brains.
It is almost safe to assume that this process was the first by
which hides were preserved in a state differing from their original
condition, the oxidation of the fatty matters naturally producing a
partial tannage. The effect of smoke may also have been discovered in
the earliest days of skin-curing, and it is reported that even now
one or two tribes use smoke to preserve skins.

The somewhat imperfect preservation of the hides by this method would
lead to further experiments being made, which evidently resulted in
the discovery of the tanning effect of leaves, twigs, and barks of
trees when soaked in water. It may be that the preservative effect
of alum was discovered even before the vegetable tanning process,
for the original Japanese white leather was made simply by steeping
the raw hides in certain rivers which contained a bed-rock of alum.
This primitive process is even followed to-day in one or two places
in Japan, but the leather is afterwards treated with oil to impart
tensile strength and increased suppleness. Strictly speaking, these
hides are not leather when finished, and they are quite unsuitable
for boots; but, being the toughest material known in the leather
trade, with the possible exception of raw hide, it is particularly
suitable and chiefly used for brace ends, and occasionally for
ladies' belts. It must not be inferred from reference to this process
that the Japanese only use this earliest method of making leather;
on the contrary, they are producing all classes of leather, and
especially belting and sole, by modern European methods, and it may
not be long before their competition with American and European
productions becomes an accomplished fact.

The available information seems to show that, until about thirty
years ago, the development of the industry was mainly the result
of accidental discoveries, and that the theory of tanning and
leather-dressing was imperfectly understood until within quite recent
times. Records of the leather trade 300 years ago prove that the
methods then in vogue were of the rudest kind; further, they show
that the practice of skimping the tanning process was not unknown
in those days, for a contemporaneous author describes the horny
condition of some of the leather which, despite the Government
inspection, appeared to have passed into the old Leadenhall
market for sale by the simple operation of "greasing the fist of
the seller." Spain and Hungary had by that time established the
manufacture of morocco and curried leather on a fairly sound basis,
while a few years later France began to develop the industry of
leather manufacture. Until about twenty years ago, waxed calf,
crup, calf kid, and alum-tanned kid were staple upper leathers,
together with the old Spanish cordovan leather. The sole leather
used in England was chiefly the output of tanneries in the United
Kingdom. About twenty years ago, however, the successful application
of the chrome tanning process caused quite a revolution in the
leather trade, with the result that about nine-tenths of the world's
production of boot upper leather is chrome-tanned. The introduction
of this process on a practical scale gave a great impetus to the work
of chemists, who have since made some remarkable discoveries and have
placed the art of leather manufacture on a scientific basis.

The old methods, however, are by no means obsolete, and it is
somewhat remarkable to find that a British patent was taken out last
year (1914) for converting hides and skins into leather by treating
them with brains and smoke.



CHAPTER II

HIDES AND SKINS


The hides and skins of animals form the principal raw material of
the tanner. Technically, the term "hides" is applied to the skins of
the larger animals, while the word "skins" is used in the case of
the smaller animals. Thus, the tanner speaks of ox, cow, bull and
horse _hides_, and of calf, sheep, and goat _skins_. There is an
intermediate size between a full-grown calf skin and a small hide,
and this is known as a "kip," but the line of demarcation is not very
clear.

Buyers often settle the difficulty by examining the growth marks
and the irregular substance of the skin, and, if these are marked
features, it is classified as a kip. The condition of the hides of
cattle is usually inferior during the six months after the animal
has become a yearling. East India tanned hides, which are largely
imported into England, are frequently described as E.I. "kips" in
the trade. This is hardly accurate, but the mistake is probably
due to the small size of full-grown Indian hides, which are very
little larger than the average European kips. It is interesting
to observe that furriers always refer to both their raw material
and the finished product as skins, irrespective of the size of the
fur-bearing animals. Most of the skins of wild animals are dressed
without removing the hair or fur, and this is quite a distinct trade
from leather manufacture, the only exception being the dressing
of closely cut and fine-haired calf skins for slippers and fancy
articles.

Practically every country in the world contributes to the supply of
hides and skins, but there are a few countries which are far in
advance of the others in the industries of cattle and sheep-raising.
The sources of tanners' raw material have undergone great changes
since the establishment of freezing and chilling stores for the
preparation of meat for export, and the market prices of hides are to
a large extent controlled by the supply in North and South America,
South Africa, and Australia. Whether or not the concentration of
these huge meat works into two or three centres is likely to benefit
the leather trade is a debatable point. The flaying, trimming, and
curing of hides in these establishments are certainly superior to
the work done by the average butcher, while, owing to the large
numbers of cattle slaughtered, the hides can be closely selected. On
the other hand, the value of hides and skins has risen enormously
in the last decade, the period coincident with the rapid growth
of the chilled and frozen meat industry, but the increased use
of leather in many directions may be mainly responsible for the
higher cost of the raw material, although it is obvious that the
concentration of the chief supplies of hides in a few lands must
tend to increase the severity of the competition among buyers. Apart
from the high prices of the hides, the concentration of the meat
industry in large chilling and freezing works has had the effect
of increasing the prices of beef and mutton, which are now higher
in price than freshly-killed English meat was a few years ago.
It appears to have been a grave error on the part of the British
Government when they stopped the imports of live cattle owing to the
fear of foot-and-mouth disease being communicated to domestic herds.
The disease has broken out in several places since the embargo was
imposed, so that the theory that the infection was only carried by
imported live cattle has been clearly disproved. The butchering of
cattle provides a large amount of work in subsidiary industries,
and the Government embargo on the importation of live cattle has
caused a great deal of distress in Deptford and Birkenhead, where
large abattoirs were erected for the reception of live cattle, which
used to be imported in fairly large numbers. There is no danger
of foot-and-mouth disease getting beyond the abattoirs or of the
slaughter of diseased cattle for food, and both tanners and butchers
hope to see the removal of the embargo. So far as possible, each
country should raise its own cattle to provide its own meat supply,
and this principle is recognised by many countries which prohibit the
import of foreign meat: but, owing to the rapid growth of populations
in industrial countries, with the consequent increase in the value of
land, it has become impracticable to raise enough cattle to supply
domestic needs. Even the United States of America, which formerly had
a great cattle-raising industry, has lately been obliged to import
live cattle to meet the requirements of its inhabitants. Similar
conditions prevail almost throughout Europe, and tanners have to look
to South America, Australia, and Africa for large supplies of raw
hides, although there are still some tanners in the United Kingdom
who use only the hides produced in this country.

The bulk of the production of hides and skins in the United Kingdom
is disposed of at weekly public auctions in the principal towns:
London, Manchester, Liverpool, Leeds, Birmingham, Newcastle, and
Glasgow being the largest centres of distribution. However, there
is still a large quantity bought by private treaty, and opinions
are divided as to which is the better method of buying. Before the
establishment of public auctions, hides were very cheap, but tanners
were unable to get a good selection, although, for sole leather, that
was not a very important matter. Public auctions have become so
firmly established that it would be impossible for tanners to revert
to the old system even if they desired it. The competition of private
buyers with the auction markets has certainly benefited the butcher
at the expense of the tanner, and the weighing and classification
of hides ultimately became so irregular in many markets that the
Tanners' Federation of the United Kingdom had to take strong
action not long ago to protect their interests. They demanded the
appointment of an independent inspector at each market to check the
weighing and sorting of the hides, but this was successfully resisted
by the market proprietors, who eventually agreed to the tanners
appointing travelling inspectors to visit the markets periodically.
The system is said to have improved matters.

The English markets do not collect enough hides to permit their close
sorting, so that, while the hides are graded according to weight and
quality and the sex of the animal, the question of varying substances
is generally ignored. There is usually a difference of 10 lb. in each
class where the hides are sorted by weight Ox, cow, heifer, and bull
hides are sold separately, as each sort has a different value. Bull
hides are comparatively poor in quality, owing to their irregular
substance and strong growth marks in the neck. Ox hides are the most
suitable for sole leather and belting, while cows' and heifers' are
used mainly for dressing hides, which are finished into bag, case,
strap, and boot leathers. The hides known as Scotch and Hereford
runts are the best of those produced in the United Kingdom, as they
are well-grown, compact, and well-suited to the making of sole
leather and belting. The grading of the weight of these hides at the
auction markets is generally as follows: 100 lb. and above, 90-99
lb., 80-89 lb., 70-79 lb., 60-69 lb., 59 lb. and less. This does not
give an ideal classification, as hides vary so much in texture and
substance, and it is quite possible to find spready hides of poor
substance and quality which would be heavier than a small but compact
and well-grown hide. It would be better from the tanner's point of
view if the hides were selected according to substance and quality.
There are not many bull hides grown in the United Kingdom, and in
many markets they are not classed by weight but simply into best and
secondary qualities. Horse hides are of even less value than those
of bulls, owing to their weaker texture and irregular substance.
That part of the skin under the mane is almost worthless, while the
flanks and sides are only useful for a secondary class of boot upper
leather, although some fairly good patent sides have lately been
produced from horse hide, which is suitable for that purpose owing
to its soft grain and pliable texture when tanned. The most valuable
part of a horse hide is the butt, which consists of the part known
as the "shell." This shell is covered with an extremely fine grain
which is not found in any other part of the hide. The well-known crup
leather is made from the shell of the horse hide.

In addition to hides, there are fairly large quantities of calf
and sheep skins sold at the weekly auctions, but veal is not such
an important article of food in England as it is on the Continent.
Sheep skins are far more numerous, as Great Britain is a big
mutton-consuming country. Home supplies of both hides and skins have
been greatly reduced, however, by the immense import of frozen and
chilled meat.

Although the domestic supply of hides and skins is quite inadequate
to meet the needs of British tanners, a large proportion is exported.
American tanners buy large quantities of the best hides and pickled
sheep skins. The latter are dewoolled and preserved by a process of
pickling with formic or sulphuric acid and salt before exportation.
Those preliminary operations are the work of the fellmonger. Nearly
all of the horse hides produced in the United Kingdom are, or were
before the War, sent to Germany, and British leather-dressers appear
to have lost the art of finishing horse hide, or are unable to
convert it into leather profitably.

The interchange of raw hides between various countries, and even
between those where leather manufacture is an important industry, is
somewhat remarkable, and only goes to prove that the concentration
of a particular industry in one or two centres of the world gives
these places a great advantage in regard to labour, organisation,
and technical skill, even over those countries where the raw
material is plentiful. Theoretically and economically it should
be advantageous to establish tanneries close to the supply of raw
hides, since the latter, under present conditions of preservation,
steadily deteriorate from the time they are removed from the carcase
until they reach the tannery. In some countries the methods of
preserving hides are actually so bad that the hides have often lost
half of their value before the tanner gets them. Two or three of the
largest American meat-packing establishments have erected or taken
over tanneries to deal with raw hides, one of their by-products.
Tanneries have also been erected near some of the large meat works in
the Argentine, but the development of the leather trade there is by
no means rapid, and at present the United States of America is the
largest leather-producing country in the world. Germany, France, and
the United Kingdom come next in the order named.

South Africa is an important source of supply of raw material, and
large quantities of Cape hides are sent to England. The production of
raw hides there is likely to be on a very large scale in a few years'
time, as the raising of Afrikander and other breeds of cattle is sure
to become an important industry now that the ravages of the terrible
disease, known as "tick," have been checked. China is another large
hide-exporting country; most of the hides from this source are
dried in the open air and are generally arsenicated to prevent the
ravages of insects. Immense quantities are also provided in all
other populous countries, but the demand for leather is generally
greater than the production of raw material in those countries. India
is a noteworthy exception to this general rule; the production of
Indian hides is enormous, and, although the leather trade is being
developed, there is a large surplus of raw hides and skins for
export. Large quantities are roughly tanned, however, and exported to
England, Germany, France, and other European countries to be dressed
and finished. The greater proportion of these hides and skins is used
for the making of shoe leather, while a good quantity is used for bag
(hide) and imitation morocco (goat) leathers.

Naturally, there is in the aggregate a considerable supply of raw
hides and skins from other parts of the world in addition to that
from the countries specially named, and new sources are being
frequently found.

It would be impossible to describe the characteristics of the
numerous varieties of hides and skins except in a full-sized
text-book, but a brief description of the principal sorts may be
given.

Some of the varieties produced in the United Kingdom have already
been described. In the main, there is not a great deal of difference
in the hides of various breeds, but there is a type of well-grown and
stout hides specially suitable for sole and belting leather; this
class is known as runts, and these hides are obtained from the Scotch
and Hereford breeds of cattle. The Scotch runts from the Highland
cattle are more valuable than any other class of hide found in the
United Kingdom; unfortunately, the production is small. Irish cattle
also yield good hides, but in England the interests of the cattle
owner, or feeder, are in conflict with those of the tanner, for the
system of artificially fattening cattle with oil cakes tends to make
the hides very greasy and weaker in the fibres than those hides from
animals which are reared on natural food-stuffs.

This grease is very difficult to remove and reduces the selling value
of sole leather by about 2d. per lb. The use of a borax solution for
soaking partially removes the grease, while it has been proposed that
the pelts should be treated with a solution of hyposulphite of soda
just before placing them in the tan liquors. A drawback of the latter
process is that a little weight is lost in the finished leather.

The trouble caused by the presence of a large quantity of natural
grease is even more pronounced in sheep skins than in cattle hides.
Naturally, a sheep arrives at maturity in about two years; but by the
modern system of intensive feeding with oily food-stuffs it can be
fattened in about ten months. This is obviously a great advantage to
the sheep-breeder; in other respects it is an unsatisfactory method,
for the mutton is not so well matured, and, therefore, is not so
nourishing; it contains too large a proportion of fat, and the skins
are very greasy and weak in fibre. The excess of grease does not
detract from the value of the wool, and may even be beneficial.

There are several varieties of sheep in the United Kingdom, with
widely different characteristics. A fellmonger should have a
good knowledge of the skins of various breeds in order to buy the
particular sorts that will meet the requirements of his customers,
as his business is to separate the wool from the skins and to
supply the former to the woollen factories and the latter to the
leather-dressers. He has, therefore, to study carefully both the wool
and pelt markets. While some breeds of sheep yield fine long wool of
bright lustre, others have comparatively short-stapled, and "kempy"
wool. Between these two classes, there are numerous grades, and the
task of sorting the various qualities of wool in those fellmongeries
where several classes of skins are worked is by no means easy. It is
a generally accepted axiom that the pelt (_i.e._, the skin denuded
of wool) is weaker in fibre in those skins which yield the finest
and best wool. In support of this, the Welsh mountain sheep may be
cited. This sheep has short, curly wool, but its skin is tough and
strong on the grain. In fact, it is about the only breed suitable for
roller leather, which is used in the cotton industry for covering the
drawing rollers of spinning-machines. Most of this leather is made in
North Wales, whence it is exported to every country where the cotton
industry is carried on.

Notable exceptions of the general rule regarding the relative
qualities of wool and pelts are found in two or three English
varieties, namely: the Lincolns, Leicesters and black-faced Suffolks,
which produce both fine wool and large pelts of good quality.

Other useful British breeds are the Southdowns, Devons, Shropshires,
Wensleydales, Scotch black-faced, Cotswolds, and Kerrys. Of the
imported varieties, the New Zealand and Cape sheep skins are the
best. The former, principally merino stock, not only provide very
fine wool, but also pelts of choice quality and large pattern.
Although the quality of the wool of Australian merino sheep is
little, if any, inferior to that of the New Zealand type, the skins
are not so good in quality, due, no doubt, to the hotter climate,
which is favourable to the breeding of insects and other pests which
damage the skins. The Cape sheep provide a skin which is quite
different in texture from that of any other breed. It has a certain
looseness of texture and softness of grain which make it particularly
suitable for the manufacture of glove leather.

South America is another large sheep-breeding country; but the skins
of this variety are not largely imported into England, most of them
being sent to Mazamet, the great centre of the fellmongering industry
in France. Buenos Aires skins are the most favoured of the South
American skins, owing to their large size and good substance. Monte
Videos are also very fine skins.

Smyrnas and Bagdads are other well-known varieties, but they are
generally imported in a rough-tanned condition, or, as it is known
technically, "in the crust." Leather-dressers finish them for
various purposes, but mainly for boot and shoe lining leather. When
properly tanned by the natives, these skins produce a supple finish,
especially those of the Smyrna variety. Unfortunately, many lots are
merely coloured on the surface with the tan liquor, with the result
that they dry hard and tinny; such partially-tanned leather is very
difficult to finish and is rarely satisfactory. Even when the tannage
is completed elsewhere before finishing them, they never produce such
good leather as skins properly tanned in the first instance.

Russia is another important country for the production of all kinds
of raw hides and skins suitable for leather manufacture. American
tanners buy very largely from this market, and a few enterprising
firms even send their own representatives to the great annual fair
held at Nishni Novgorod, where large quantities of dried hides and
skins, besides many other kinds of produce, are offered for sale.
British tanners take comparatively little interest in this important
supply, but, as a result of the great European War, an increase of
trade between Russia and the United Kingdom is anticipated, although
the Russian leather trade is developing rapidly and will absorb
increasing quantities of native raw material.

Excepting a few in Ireland, raw goat skins are not produced in Great
Britain. The chief drawback to goat breeding there is a somewhat
inexplicable aversion on the part of the public to the flesh of
goats; although another reason may be the destructive nature of the
animals themselves, for they devour and uproot anything edible that
comes in their way. It is, perhaps, unfortunate that some of the
large areas of uncultivated land in Great Britain are not given up
to the breeding of goats on a large scale, since these hardy animals
will thrive on rough, hilly lands. Apart from the value of the meat,
it might be a paying proposition to rear large herds of goats for
the supply of milk (which is more nourishing than cows') and skins.
Leather-dressers are, therefore, dependent on imported supplies,
of which the principal sources are India (North-Western District),
Mexico, Arabia, Africa, South America, and several European countries.

Goat skins from the main sources of supply vary very much in
quality--even those produced in the same country. In India, for
example, skins may be obtained in some districts which can be made
into leather to sell at about 5d. per square foot; from another
district, when finished into the same kind of leather, say glazed
kid, they may be worth 1s. 4d.[1] per foot. Fineness and clearness
of grain and good substance are the main essentials of a first-class
goat-skin leather; unfortunately these qualities are rarely combined
in one class of skin, and there is a decided surplus of light thin
skins which are hardly saleable, even for ladies' shoes. Some
American shoemakers overcome this difficulty by pasting a piece of
cloth on the back of the skin. In fairness to the buyer, the boots
made of such leather should be specially marked, as the wearing
quality of a backed thin leather is not to be compared with one
naturally stout.

  [1] It must be understood that, owing to the war, these prices
  have been greatly increased.

The skins of goats are used for many purposes besides the
manufacture of the famous glacé kid leather; gloves, moroccos for
bookbinding, upholstery for furniture, fancy articles such as purses,
pocket-books, bags, and ladies' belts all require large quantities of
goat and kid skins. It may be pointed out here, however, that quite
nine-tenths of the so-called kid gloves are made of lamb and sheep
skins. In appearance, there is very little difference between the
real kid and the lamb skin gloves, but the former are more durable
and warmer in wear than the latter.

With an enormous range of qualities, it is a difficult task for the
goat-skin dresser to find the most suitable sorts for his trade.
The skins used in the glove industry are largely obtained from
the Near Eastern countries, Arabia, Austria, Spain, and the Cape.
The selections best suited to the making of glazed and "patent"
(japanned) kid are found in the North-Western provinces of India,
Brazil, China, Russia (especially the Asiatic provinces), Mexico,
the Cape, and Arabia. The Indian goats known as the Patnas, which
are collected in the district of Behar, are commonly supposed to
be the best in the world, chiefly because of their fine grain and
stout substance; but the best Brazilian and Mexican skins are
equally good in quality. The best moroccos for fancy articles are
made from Continental skins, and in this respect Germany has the
great advantage of a good supply of native skins. Norway and Spain
also provide skins suitable for real morocco leather. A very large
quantity of Indian-tanned goat skins are imported into European
countries and dressed for "morocco" leather. There should be a
distinctive name for this class of leather, as, although it is
similar in appearance, it is not nearly so good in quality as the
real morocco.

In addition to cattle hides, sheep, and goat skins, which are the
main supply of raw material for leather, other kinds of hides and
skins are utilised. Horse hides, which, in the United Kingdom, are
graded according to size and quality in four or five selections and
sold by the piece, are largely used on the Continent, and especially
in Germany; nearly all of the British production being sold to that
country. When chrome tanned, these hides produce quite a serviceable
upper leather of good wearing quality, but, owing to their somewhat
loose texture, the characteristic grain of box calf cannot be
reproduced naturally, and the surface of the leather has, therefore,
to be printed. This style of finished leather does not meet with the
favour of British boot manufacturers, and the industry has not been
greatly developed in consequence. In view of the increasing cost of
other kinds of leather, however, more attention may be paid to that
made from horse hide, but the supply of this raw material is very
small compared to the production on the Continent, where horse flesh
is consumed freely. Russia produces large quantities of horse hides
and colt skins, most of which are exported to the United States of
America, where they are made chiefly into japanned, or so-called
"patent," leather, which commands a very high price in relation to
the cost of the raw material.

Next in importance to horse hides is the pig skin, which produces a
wonderfully tough leather. The pig skin leather industry is chiefly
confined to Scotland and Germany, the reason being that the skins are
left on the carcases in the other parts of the world. On the average,
a pig skin is worth about 6s., yet it is seldom removed from the
carcase. One reason is the great difficulty of flaying the animal; it
appears to be almost impossible by present methods to remove the skin
without cutting away a large quantity of fat, and the value of the
skin compared to the loss of weight of the meat offers very little
inducement to remove the skin, in addition to which, the custom of
leaving the rind on bacon and pork effectually prevents any attempt
at present to increase the supply of pig skins. This is a great loss
to the leather trade, for the pig skin is particularly suitable for
saddles and various kinds of strong leather goods. Imitation pig-skin
leather is made from hides, shoulders, bellies, or persians, but real
pig skin is distinguished from the imitation by its peculiarly marked
grain, formed of groups of three small holes which penetrate well
into the skin and form part of the sheaths of the pig's bristles.

Among other skins useful for leather are those of the wallaby,
kangaroo, dog, lizard, crocodile, alligator, ichneumon, frog
(Japanese), deer, antelope, and chamois, while it is said that even
rabbit skins have been pressed into service in Germany, though they
cannot have much value owing to their small size and thin substance.
Dog-skin leather wears well, mainly on account of the large amount of
natural grease present in the skin, but the supplies are naturally
small. The hides of the walrus, elephant, rhinoceros, hippopotamus,
and other wild animals are also tanned in small quantities, walrus
leather being well adapted for knife and sword polishing.

The mammals also contribute their quota to the supply of raw material
of the leather trade, the seal perhaps, being the most important.
This refers to the hairy seal hunted off the North American coast.

The raw skins are shipped chiefly from Newfoundland, where the
industry of seal fishing is well organised and provides employment
for about 6,000 men. The seal caught in the North Atlantic Ocean is
hairy and quite distinct from the fur seal captured in the Arctic
Ocean off Alaska. The skin of the hair seal is only suitable for
making into leather, but there is a layer of fat underneath it which
furnishes a valuable raw material for the manufacture of oils and
soap. The skins are salted and shipped to America and England. They
are easily distinguished from other kinds of commercial hides and
skins by the oily appearance of the flesh side.

According to an American Consular Report, the results of the fishing
during the season 1913 were satisfactory. The total number of seals
captured was 272,965, which were valued at £98,800. The number of
skins exported was 212,285, valued at £64,300, of which the United
States of America bought 151,355, the United Kingdom 60,754, and
Canada 176.

The porpoise, or sea hog, has a very useful hide which, when dressed,
makes a tough leather suitable for laces. The hides of other
cetaceous mammals, such as the whale and narwhal, are convertible
into useful leather. The British "porpoise" laces are generally made
from the skin of the white whale (_beluga_).


DEFECTS OF RAW HIDES AND SKINS

A remarkable feature of the leather trade is the great waste due
to the careless preparation of a large number of hides and skins.
Naturally, owing to their greatly increased value in recent years,
there has been a decided improvement, but much loss occurs every day
from damage to hides which ought to be avoided. The chief faults are
in flaying and curing, but there are other important defects due to
natural causes.

Bad flaying may be due (1) to cutting holes in the hides or skins;
(2) to "scoring" or "siding" (_i.e._, cutting into the hide without
going completely through), this generally occurring in the flanks or
sides which are the most difficult parts of the hide to remove from
the carcase; and (3) to mis-shaping the hide, which ought to be left
square.

Any or all of these defects may be found in a single hide. Despite
the active work of several proprietors of hide markets and the
tanners' federations the proportion of badly-flayed hides in England
constitutes a serious loss, which, however, may not fall directly on
either the butcher or the tanner, for the former may save in wages
by employing an inexperienced slaughterman, while the tanner pays a
reduced price for the hide.

The losses due to bad flaying and curing in the United Kingdom
are mainly attributable to the butchers' preference to kill these
beasts in their own back-yard rather than in a public abattoir.
Many of these small private slaughterhouses ought to be condemned
by the authorities; but very few people outside those immediately
interested have taken the trouble to inspect a modern public abattoir
where everything is provided to carry on the work expeditiously and
hygienically. On the Continent, where the conservatism of traders is
not permitted to interfere with the public welfare to such an extent
as it is in England, public abattoirs have become quite a feature in
many cities, and one of the principal results of the system has been
a remarkable improvement in the preparation of raw hides and skins
for the tanner. In fact, a mechanical method of flaying has been
invented in Paris, and is used extensively at the public abattoirs,
by which hides are removed from cattle without a single mark or
scratch. The method is known as _dépouille mécanique_ (mechanical
flaying) and consists in forcibly removing, by means of a windlass
worked by electric power, the portions of hide which adhere firmly to
the carcase and which are found over the ribs, the buttocks, and the
tail. The remaining part of the hide can be easily removed with the
ordinary butchers' flaying knife or with a heavy hammer of special
design. The apparatus required to carry out the mechanical method of
flaying, beyond the fixtures in the abattoirs where the process is
adopted, consist of two lengths of chain to hold the carcase firmly,
two special hammers, and one pair of strong pincers; the cost of one
set is about £4. Mr. Gaston Tainturier, of Paris, is the inventor of
this system, which has added thousands of pounds to the incomes of
Parisian butchers.

Figure 1 is from a photograph taken at the Islington (London)
Abattoir, where a demonstration of the process was given by Mr.
Tainturier in February, 1913.

Naturally, this method cannot be adopted in small slaughterhouses
in back-yards, but is readily adaptable to public abattoirs, where
practically all of the heavy work is done by electrical power. This
exemplifies only one of several advantages of modern abattoirs over
private slaughterhouses.

Although it cannot be expected that the English butchers will readily
change their prejudice against modern abattoirs, they are slowly but
gradually improving the flaying process in view of the high prices
paid for perfect hides. The most progressive of the proprietors of
the English hide markets are offering money prizes to slaughtermen
for the best flayed hides. Strictly speaking, this encouragement
should come from the butcher, who receives the benefit of increased
prices for hides removed without a scratch. The Tainturier system,
however, gives better results, no matter how well the hides are
removed with the knife. The method is not patented, and it is open to
anyone to adopt it merely for the cost of the apparatus, yet, despite
this gain, no butcher outside France and Belgium has yet adopted the
method, although the trade is losing hundreds of pounds every week
through bad flaying.

Several other systems of improved flaying have been devised, and
some of them patented, but very few have been adopted on a practical
scale. One of the most useful consists of fixing a safeguard about
a quarter of an inch from the edge of the knife; this prevents the
possibility of cutting holes into the hide, although it does not,
of course, prevent scoring, which is a serious defect in hides made
into sole leather. A safe method is to use a sharp knife of hard
wood, such as hickory, which has been successfully tried in one of
the large American meat-packing establishments. The hides from these
abattoirs are generally well-flayed, properly cured, and closely
trimmed, with the result that they command higher prices than any
other class of salted hides. The quotations for "packer" hides are
followed with keen interest by tanners in all parts of the world.

  [Illustration: FIG. 1

  MECHANICAL FLAYING

  (_dépouille mécanique_)]

Another useful method of preventing damage to the hides by cuts with
a knife is that invented by Mr. E. Pim, a Liverpool hide factor.
The apparatus used is known as the tail extractor. It is of simple
construction, consisting of four pieces of iron riveted together
loosely in the shape of a diamond with a clamp attached to
secure the tail. The hide is then forcibly removed from the tail
and the buttocks by pulling it downward (Fig. 2). The importance of
this operation can be gauged from the fact that by the use of the
butcher's knife both of these parts of the hide are often cut very
badly.

  [Illustration: FIG. 2

  PIM'S SYSTEM OF FLAYING]

Even the apparently trivial matter of removing the hide from the
cheeks and face is economically important, for, unless those parts
are removed so as to get the maximum surface, they are only fit to
be cut off and thrown in a pit with other pieces and roundings which
are made into glue.

Imperfect preservation is another serious form of damage to hides and
one that cannot be easily remedied in some of the hot climates. Hides
and skins may be simply dried, salted and dried, wet-salted, treated
with arsenic solution and dried, brined or pickled with acid and
salt; of these methods the last-named is the most effective, but is
not practicable, or, at least, has not yet been applied practically
to the cure of hides and calf skins. Salt is not available, or is too
costly in most tropical countries; hence, Chinese, Indian, Mexican,
Colombian, and Arabian hides and skins are generally exported in
a dry condition. Even when the hides are dried under the best
conditions in a cool and shady place, they are of less value than a
fresh or a wet-salted hide, owing to a certain loss of gelatinous
matter in softening them before they can be placed in the lime
liquors. But it not infrequently happens that hides are dried by
exposure to the hot sun, or perhaps in a strong current of air. In
either case, the hide is much reduced in value and may be irreparably
ruined. The effect of submitting hides to these conditions is that
the exterior surface becomes rapidly dry and, naturally, contracted,
so that the air or heat cannot reach the interior, which retains
moisture. This moist inner layer may be quite thin, but it contains
sufficient nutrient to develop putrefactive organisms, so that when
the hide is soaked in water it practically falls to pieces. The
effect of hot sun or heat of any kind is, of course, disastrous to
raw hides and skins, and there have been not a few claims on shipping
companies as the result of storing hides near the boilers of ships.

Salt is almost invariably used for curing both hides and calf
skins, but though it is a good preservative it has one or two minor
defects. It contains too much water, and is liable to contain traces
of iron which is inimical to both raw hides and leather in process
of manufacture. Common salt is also liable to cause stains which
cannot be removed in later processes, and which are even accentuated
in the tan liquors. One trade chemist attributes these stains to
the presence of calcium sulphate (Ca. SO_{4}) or gypsum in the
salt, which is converted into calcium phosphate by the action of
the phosphoric acid in the nuclei of the hide on the sulphate of
calcium. Another well-known technical chemist is certain that stains
are produced by the growth of bacteria, and to prove his assertion
prepared in gelatine several cultures from salt-stained skins.
Practical men generally attribute the stains to the presence of
blood on the hides or skins at the time of curing, and the majority
of the stains are probably due to this cause, although the presence
of calcium sulphate as an impurity of the salt would undoubtedly
contribute to this defect. Blood contains a percentage of iron, and,
with other extraneous matters, should be washed from the hides before
salting them.

Fortunately, chemists have lately paid attention to the advantages
of the use of pure salt in various industries, with the result that
at least two chemically pure products are now available. The use of
these salts should be general for the cure of hides and skins, as
they are quite dry, and, therefore, easily spread. As a curing agent,
they are much more effective and lasting than common salt.

The use of glauber salts (Na_{2} SO_{4}) is recommended by the
International Commission for the Preservation, Cure, and Disinfection
of Hides and Skins instead of ordinary salt, where the latter is
unobtainable. The preparation of a sterilised salt, however, renders
its export a practical proposition to almost any part of the world.

Although the loss due to bad curing and flaying is very great, it is
quite small compared with the damage caused by natural defects.

The ravages of disease cause a great wastage of hides and skins, as
animals infected with anthrax are immediately destroyed and cremated
in all civilised countries, while, in Great Britain, foot-and-mouth
disease is kept in check by the same drastic method. In many other
countries, the infected cattle are isolated, treated with an
antiseptic hoof-and-mouth wash and generally cured, as it is a mild
fever which soon runs its course, although it is very contagious. The
germ of foot-and-mouth disease has not yet been discovered, for the
most powerful microscope fails to reveal its presence, but cattle
readily show the complaint, as their hoofs and mouths become covered
with swollen lesions.

Another kind of fever, known as "tick," was prevalent in the southern
part of the United States, but this disease was eventually eliminated
by systematically "dipping" the cattle three or four times a year.
The cattle "dip" used effectually prevented the ravages of the fly
which caused the disease. A similar method has of late years been
adopted in South Africa, with the result that cattle-raising in that
country is developing rapidly.

Anthrax is due to the presence of _bacillus anthracis_, a vegetable
organism of Siberian origin. Dry Chinese and Russian hides are
specially liable to contain the spores of anthrax, and, as the
disease proves fatal to workmen infected by it unless treatment with
anti-anthrax serum be given in the early stages, hides and skins
from infected areas should be disinfected before shipment. The method
proposed by Mr. A. Seymour-Jones, which consists in treating hides
with very dilute formic acid and one part of bichloride of mercury
in 1,000 of water, and afterwards with a saturated solution of salt
solution (.02 per cent.) of bichloride of mercury, seems to be the
most effective without damaging the hides.

  [Illustration: WARBLE FLY

  (1) Egg, (2) Larva, (3 and 4) Chrysalides, (5) Natural form of
  fly, (6) Magnified fly.]

A peculiar natural defect is found in many South American goat skins,
especially the Brazilian, which are often badly scratched by the
animals rubbing themselves against cactus plants. Although, perhaps,
more of an artificial than a natural defect, the scratches caused by
cattle rubbing their hides against barbed wire constitute a serious,
but easily avoidable, loss. Such a barbarous system of fencing ought
never to be used.

  [Illustration: A KIP CONTAINING 584 HOLES CAUSED BY THE WARBLE FLY

  (The skin belongs to W. D. Mark & Sons, Hide Factors,
  Newcastle.)]

  [Illustration: FIG. 3

  HOLE IN COW HIDE, MADE BY THE GRUB OF THE WARBLE FLY

  (Magnified fifteen times)]

The most serious loss in connection with hides and skins, however,
is caused by the warble flies, _hypoderma bovis_ and _hypoderma
lineatum_, which lay their eggs on the hides of cattle. It has been a
debatable point for some years as to whether these eggs hatched and
burrowed their way into the hides from the exterior or were licked
and swallowed by the cattle and, after traversing the digestive
tract, pierced the hide from the interior. Professor Carpenter,
who has been experimenting a number of years for the Department
of Agriculture for Ireland, has succeeded in taking a remarkable
photograph (Fig. 3) which proves that the larvae penetrate the hide
from the exterior. These develop within the hide and often penetrate
to the flesh before they fall out to the ground and change into the
fly.

The most effective way of getting rid of the pest is to destroy the
larvae, either by cutting them out and crushing them under foot, or
by piercing them with a hot needle. No satisfactory dressing has
yet been found, but Prof. Carpenter states that sulphur dioxide is
effectual, if a good method of applying it can be devised.

While sheep skins are immune from the attacks of the warble fly, they
are often damaged by the blow-fly, lice, keds, and ticks; by scab
caused by the action of a mite or acarus; and by "cockle," which
causes a wrinkled grain. The origin of cockle is not definitely
known, but it is a seasonal defect which begins to show on a large
number of skins in December and does not disappear until the sheep
are shorn in the following spring.



CHAPTER III

TANNING MATERIALS


Tanning materials are derived from the vegetable, mineral, and animal
kingdoms.

The vegetable materials used are woods, barks, shrubs, leaves, and
fruits, either in their natural state or in the form of extracts. The
majority of the minerals have a more or less tanning effect on animal
fibres, but the principal are basic chrome salts, formaldehyde, alum
and salt. Titanium, iron, cerium and potassium salts also convert
skins into leather, but are not yet used commercially.

The animal matters that will convert skins into leather consist of
oxidised oils (chamois leather), fats, and brains (crown, Helvetia,
or Preller's leather).

Each of these classes of tanning materials has characteristic effects
which render them easily distinguishable. The use of combinations
of vegetable and mineral tannins has lately increased, and it is
possible that the blending of the two classes of materials may
produce an ideal tannage for certain classes of leather. In fact,
this result is already claimed for a chemically combined tanning
material which, according to the American patent, is prepared by the
following method: 125 lb. of solid quebracho extract is dissolved
in the same weight of hot water and allowed to cool; 16 lb. of
commercial caustic soda dissolved in two or three times its weight of
water is added, and the mixture agitated about half an hour; 150 lb.
of chromium sulphate is then added. In this way an insoluble tannate
of chrome is produced, but, on boiling and agitating, it changes
to a greenish brown colour and forms a sulphotannate of chrome. The
combination of the alum tannage and gambier (a vegetable extract)
has been used successfully for years past. Another combination which
has given good practical results is the tannage with alum and chrome
salts in the manufacture of glove leather.

The vegetable materials containing tannin should be arranged
botanically, but the following classification is simpler for
practical purposes.


NATURAL TANNING MATERIALS

1. _Barks._--Oak, Hemlock, Pine, Fir, Alder, Khaki, Willow, Cork,
Mimosa or Wattle, Babool, Larch, Mangrove, Spruce, Elm, Birch,
Pomegranate, Cebil.

2. _Leaves, Twigs, etc._--Sumach, Mangrove, Mango, Eucalyptus,
Pistacia, Lentiscus.

3. _Roots._--Canaigre, Palmetto.

4. _Fruits._--Myrobalans, Valonia, Divi-Divi, Cascalote, Mangosteen,
Pomegranate, Celavinia, Bablah, Algarobilla.

5. _Excrescences._--Gall Nuts, Chinese Galls, Pistacia Galls,
Tamarisk Galls.


TANNING EXTRACTS

1. _Woods._--Oak, Quebracho, Hemlock, Chestnut, Mimosa, Mangrove,
Spruce.

2. _Barks._--Oak, Wattle or Mimosa, Larch.

3. _Shrubs, Leaves, etc._--Gambier, Cutch, Catechu, Kino, Sumach.

4. _Fruits._--Myrobalans, Valonia.

5. _Roots._--Palmetto.

Of these materials, only about twenty are of much importance
commercially, the principal being oak, chestnut, quebracho, hemlock,
valonia, gambier, myrobalans, mimosa or wattle, sumach, mangrove,
divi-divi, spruce, larch, and babool.

OAK BARK (_quercus robur_) is still an important material, but is
rarely used alone. The bark from English oaks contains from 8-14 per
cent. of tannin (quercitannic acid) as estimated by the impregnation
of a standardised hide powder in a given quantity of the tanning
material in solution. Owing to its weakness in tannin compared with
other materials, oak bark tans very slowly. Used for sole leather,
it would not produce the essential quality of firmness and solidity,
and it is now customary to use a stronger tanning material, such as
valonia, or valonia extract, or gambier in the latter stages of the
process. This is the nearest approach to the pure oak bark tannage of
former days, and, if carefully regulated, is a great improvement on
the old method.

If dressing hides and calf skins required for boot upper leather are
bark-tanned, the tannage is often completed in a sumach liquor, the
object in this case being to lighten the colour so that the leather
can be dyed evenly.

In England, oak bark is harvested in April and May, when the sap
rises in the tree. Rings are cut round the tree soon after it is
felled and the bark is peeled from the tree with a special tool which
is forced between the bark and the wood. It is peeled in narrow
strips about 3 ft. in length, and on delivery to the tannery is
stacked in huge ricks. If harvested in a good, dry condition, the
bark is said to improve with age, although analytical tests have
shown that there is always a certain loss of tannin. An old rick is
much darker in colour than a new one, owing to exposure to the air.
Coppice bark from young trees is preferred by tanners, as it is free
from ross and generally contains more tannin than the rough bark.

In view of the modern demand for materials in extract form, English
oak bark would almost certainly be preferred in the form of a
concentrated liquid, if the supply of the raw material was plentiful
within a limited area. During the last few years it has not met with
a ready sale, owing to the large supply of other materials, but it
would doubtless regain some of its former popularity if it were
prepared in the form of an extract containing about 25 per cent.
of tannin. The only oak bark extract on the market is the American
chestnut oak (_quercus prinus_).

OAK WOOD is very largely used for the manufacture of tanning extract,
especially in Hungary and Canada. The extract contains from 24-28
per cent. of tannin, and is extensively used in the tannage of heavy
leathers, as it strengthens the liquors and hastens the process,
while keeping the quality of the leather at a high standard.

VALONIA (_quercus aegilops_) is the acorn cups of an oak tree which
grows abundantly in Asia Minor and the Greek Archipelago. No other
part but the acorn cups is exported. The harvest in Asia Minor takes
place in August, when the fruit ripens and the cups can be easily
beaten from the trees. They are left to dry on the ground and are
then sent to stores in seaport towns, and principally to Smyrna. The
drying is still further completed in spacious warehouses, where the
cups are spread out and turned over until fermentation ceases. During
this process the acorns shrink and are rejected. The cups should be
perfectly dried and very hard before export. The Turkish valonia
contains from 30 to 35 per cent. of tannin, and is of much better
quality than the Greek, which is usually harvested before it is ripe,
and, therefore, contains the acorn. As the acorn has practically no
tannin value, the Greek valonia contains only 25 to 28 per cent.
tannin. There are several grades of valonia, the best going to
Russia, Austria, and Italy. English tanners seem to prefer the lower
qualities at present, probably because the price is much less than
that of the best grade.

The beard of the valonia cup is much richer in tannin than the shell,
and, as several of the spines become detached during the storage of
the material, there is always a certain quantity of beard (_trillo_)
on offer. This may contain up to 42 per cent. of tannin, but its
price is usually the same as that of ordinary valonia. Of late years,
very large quantities of valonia have been made into extract at two
works in Smyrna. The production of extract will no doubt increase,
with a corresponding reduction in the export of the raw material.
The great advantages of the extract over the natural cup are its
superior strength of tannin (60 to 65 per cent.), easier solubility,
uniformity of quality, lower cost per unit of tan, and guaranteed
purity.

Valonia is well adapted for the tannage of sole leather in
conjunction with oak bark, for it deposits a heavy bloom (ellagic
acid), imparts weight and solidity, and increases the resistance of
the leather to moisture.

THE CHESTNUT TREE (_castanea vesca_) probably provides the next
tanning material of importance. This must not be confused with the
chestnut oak, an American tree which also yields a very useful
tannin. The chestnut is indigenous to the South of France and Italy,
where the forests have been considerably reduced in size to meet the
great demand for this popular tanning material. The greater part of
the denuded forests have not been replanted with the chestnut, as
the land has been put under cultivation whenever possible. A further
depletion has been caused by the ravages of an insect, which turns
the interior of the wood quite black and renders it unfit for
tanning purposes. It will, naturally, be several years before the
supply is exhausted, even if no reafforestation is undertaken. As
it is the most important tanning material grown in France, and the
chestnuts are used as a food, steps may be taken to cultivate the
trees on areas unsuitable for agriculture. Liquid chestnut extract
contains from 30 to 32 per cent. of tannin, and, when decolorised,
gives a light brown colour to the leather. It is rarely, if ever,
used alone, but generally in conjunction with quebracho, valonia or
myrobalan extracts.

THE CHESTNUT OAK TREE is indigenous to America and the wood yields a
very good tanning extract, containing up to 30 per cent. of tannin.
This material is the principal tanning agent used in America, where
the tannages are roughly classified in three sections: (1) oak, (2)
hemlock, and (3) the union (_i.e._, a mixture of hemlock and oak).
American tanners also use other materials to a smaller extent,
chiefly for blending with the principal tannins. Quebracho and spruce
extracts are specially favoured.

QUEBRACHO COLORADO is a tree indigenous to South America, the best
wood for tanning purposes being found in the Gran Chaco district in
the north of Argentina, and in Uruguay. The wood contains from 17 to
22 per cent. of tannin, and is so hard and heavy that it sinks in
water. In fact, its name is derived from two Portuguese words meaning
"axe-breaker."

After felling the trees, they are cut up into logs about 4 ft. in
length and either exported in this state to Hamburg, Havre, and
Liverpool, or sent to the numerous factories in close proximity to
the forests to be made into extract, in which an enormous trade has
of late years been developed. Very little of the natural material
is now used, as, even after cutting the wood into chips, the tannin
is extracted only with great difficulty, whereas the extract can be
treated with sulphites, alkalies, or neradol (the artificial tannin)
to render it easily soluble, besides which the concentration of the
material raises the percentage of its tannin to 65 or even 70 per
cent. Owing, perhaps, to faulty preparation, this tanning extract was
not well received at first, but it is now among the principal tannins
and increases in importance every year.

MYROBALANS is the unripe fruit of an Indian tree (_terminalia
chebula_) and contains from 35 to 40 per cent. of tannin which gives
a light colour to leather. This material is useful both for light
and heavy leathers, but is generally used in admixture with other
tannins. It deposits much bloom (ellagic acid) and is largely used
for brightening the dark colour produced by other tannins. A large
quantity of this material is now made into extracts, which are
more convenient to handle and more uniform in strength of tannin.
Natural myrobalans have the appearance of shrivelled nutmegs, except
that they are yellowish in colour; they are very hard and require
a special milling machine to reduce them to powder. The quality of
myrobalan nuts varies in different districts, the best being Bhimlies
and Jubbalpores.

SUMACH is a valuable tanning material, and is used for a large
proportion of the light and fancy leathers. It is a small bush plant
which grows in Italy, Spain, Southern France, America, and Algeria,
but of the numerous varieties the Sicilian (_rhus coriaria_) is by
far the most important. Sumach is one of the few materials cultivated
on an extensive scale; most tanning materials are derived from
natural sources and, chiefly owing to the length of time before trees
reach maturity, it would not be a paying proposition to cultivate
them. The sumach shrubs are propagated from small cuttings and
the leaves can be picked at the end of the first year, but it is
better to allow the shrubs to become more firmly established before
stripping them. The leaves are dried and sometimes exported whole,
especially for the use of the silk manufacturers in Lyons; but
they are more often ground to a fine powder. All sumachs should be
ventilated to remove foreign matters and all traces of iron, which
would cause dark bluish stains on the leather. "Ventilation" is
effected by passing currents of air, preferably with a fan, through a
narrow room, when the pure sumach is sent forward, while the heavier
particles of dirt and small pieces of wood remain behind. Sometimes
the process is repeated, and the best brands of sumach are generally
described as "pure, extra ventilated." As far as possible, the male
plants (_mascolino sommacco_) are cultivated in Sicily, where the
best sumach is grown. Female sumach (_femminello sommacco_), grown in
parts of Italy, is weaker in tannin than the male, but is rarely sold
separately. The serious amount of adulteration formerly practised
by the admixture of inferior plants, and particularly of lentisco
(_pistacia lentisco_) led to the Italian Government taking strong
action a few years ago, and it is now possible, for a very small sum,
to have any consignment inspected and analysed by the Government.
Lentisco is now sold separately and is used for common work.

Sumach has been successfully introduced into Australia, but its
development is retarded owing to difficulties of labour, which render
competition with the European product almost impossible. An inferior
sumach (_rhus glabra_) is grown in America, chiefly in the State of
Virginia. It contains from 15 to 20 per cent. of tannin, and produces
a darker coloured leather than Sicilian, the best qualities of which
contain 27 to 30 per cent. of tannin.

A useful test for finding out if a sumach has been adulterated is to
treat a small quantity with strong nitric acid, which destroys the
structure of the leaves. The mass is washed and neutralised with an
alkali, when the appearance of the midrib and veins of the leaves of
the common adulterants are easily recognised.

Sumach is not so much used for shoe upper leather as it formerly
was, but it is the best tanning agent for many kinds of fancy light
leathers, such as bookbinding, calf, and skivers (the grain of split
sheep skins), moroccos, furniture leather, etc. It is also less
subject to the action of the air and gaslight than any other tanning
material, and is strongly recommended for tanning purposes by a
special committee appointed by the Society of Arts to enquire into
causes of the rapid decay of leather bindings. Sumach is very useful
for brightening up the colour of leather tanned with darker tannins,
and is frequently used for improving the colour of both dressing and
sole leather. By itself, it yields an almost white leather which
affords a good foundation for the most delicate shades.

GAMBIER or TERRA JAPONICA (_uncaria gambir_) is a crude extract of
a shrub indigenous to the Malay Peninsula. Nearly the whole of the
production is shipped from Singapore. The leaves and twigs are boiled
in an iron vessel, and when the mass has become syrupy it is strained
through a rough sieve into a shallow tub, where it is cooled. The
liquor is stirred while cooling and rapidly thickens. Before it sets,
it is cut into 1 in. cubes and thoroughly dried. Good qualities
contain from 50-65 per cent. of tannin. An inferior product, called
"block gambier," is made by allowing the syrupy mass to set in large
blocks weighing about 2 cwt. each. These are packed in coarse
matting. The strength of tannin varies from 30 to 40 per cent.
Gambier is a good tanning material, but its use has been declining
for some years past owing to its being frequently adulterated with
sago and other farinaceous plants. However, a pure gambier extract,
manufactured on the latest scientific principles, has been placed on
the market, and there will undoubtedly be a revival of the use of
this valuable tannin. This pure gambier is prepared at Asahan, in
Sumatra, and is guaranteed to contain a minimum of 38 per cent. of
tannin.

Gambier can be used to advantage in keeping up the strength of bark
liquors in the tannage of sole leather and hastening the process,
while it may be used alone for the tannage of boot upper leather
and dressing hides. It produces an exceptionally mellow and plump
leather. It is preferable, however, to complete a gambier tannage
with a little oak wood or quebracho extract, in order to fix the
tannin principle of gambier, which, perhaps on account of its
viscosity, does not readily combine with the fibres of the skin.

MANGROVE or MANGLE, a tree found on the coasts of several tropical
countries, yields a useful bark for tanning purposes. At low tide,
these trees show their great arched roots standing high above the
ground. The best varieties, the _ceriops_ species, are found in the
East Indies and Bengal, and the bark of these is said to contain
sometimes nearly 40 per cent. of tannin. Other varieties contain from
15 to 25 per cent. The bark is generally made into a solid extract,
or "cutch," in which form it contains more than 60 per cent. of
tannin, It is useful to blend with other materials, such as oak wood,
chestnut, and quebracho extracts, but used by itself it imparts a
strong reddish colour to the leather. Some of the Indian varieties
are used as dyeing materials, and act as a satisfactory mordant in
dyeing leather a dark shade.

MIMOSA or WATTLE trees, which belong to the _acacia_ species,
yield bark rich in tannin. Australia is the native country of
several varieties, including the Black Wattle (_acacia pycnantha_),
the Golden Wattle (_A. longifolia_), and the Green Wattle (_A.
decurrens_).

The bark contains from 20 to 45 per cent. of tannin. The cultivation
of wattle in Australia seems to have declined, owing to the high cost
of labour and inability to compete with the mimosa bark imported from
South Africa, where it is cultivated on a very large scale and where
labour conditions are more favourable for the growers, as is clearly
shown by the fact that the wattle growers in Australia successfully
petitioned the Government a short time ago to place a duty of £1 10s.
per ton on the imported bark.

The introduction of the industry into South Africa was quite an
interesting adventure. A Mr. Vanderplank brought the seeds from
Australia to England about seventy years ago, and afterwards took
them to South Africa, where, in recognition of certain services a
few months after his arrival, he was granted a farm by the Dutch
Government. He then planted the seeds of the black wattle, which grew
so well that it was only a question of developing the industry. It
was some years before any African bark was exported, and only £11
worth was shipped in 1886. In 1911, the exports had risen to £288,000.

Wattle trees can be grown on soil that is unsuitable for agriculture,
and there is every prospect of the industry expanding in South
Africa, where a factory has lately been established for the purpose
of converting the bark into an extract, which, it is said, will
contain between 50 and 60 per cent. of tannin. By far the greater
proportion of wattle bark is still exported in the natural form,
ground or chopped, and packed into bags weighing about 1 cwt. each.
Before the European War nearly the whole of the bark was shipped to
Hamburg, English tanners taking very little interest in it, although
it was largely used by German tanners. But since the supplies of
the materials favoured by British tanners have become somewhat
restricted, attention has been drawn to the value of mimosa bark.

DIVI-DIVI (_caesalpinia coriaria_) is the dried pods of a Central
American tree. It has also been successfully cultivated in India. The
pods are rich in tannin, containing anything from 40-50 per cent.,
but its value is discounted by its liability to fermentation, which,
however, may be checked to some extent by the use of antiseptics,
such as carbolic acid, formaldehyde, or by the addition of synthetic
tannin, neradol. If this tendency to fermentation and oxidation of
the colouring matter could be checked completely, divi-divi would
be a valuable material, as it makes a firm leather of good colour.
When dried, the pods curl up in the shape of the letters S and C. The
tannin is found in the husks of the pod. The seeds, which contain
no tannin, are so hard that it has not yet been found profitable
to extract the oil from them. Very similar tanning materials to
divi-divi are cascalote, indigenous to Mexico, and algarobilla
(_caesalpinia brevifolia_) which grows in Chili. Cascalote is chiefly
used by Mexican tanners and is rarely exported. Algarobilla is not
available in large quantities, otherwise it would be largely used in
Great Britain, as it does not ferment so readily as divi-divi, and is
even richer in tannin.

CELAVINIA (also spelt celavina and cevalina) has been on the English
market since 1905, but has only lately been sold in large quantities.
The scarcity of some of the popular tanning materials since the
outbreak of the European War resulted in enquiries for materials that
were very little known, and celavinia has proved worthy of attention.
It consists of the seed pods of the tree _caesalpinia tinctoria_,
which grows abundantly in certain districts of Central and South
America. The pod is from 4 to 6 in. long and is flaky when dried. It
contains 30 to 32 per cent, of tannin of the pyrogallol class, and
gives a very light-coloured and almost white leather. It is the only
pyrogallol tannin which does not deposit bloom, or ellagic acid, on
the leather. It may be used as a substitute for sumach in tanning,
but has not the same bleaching effect in the retanning process. A
tanning extract of celavinia would be useful for some classes of
light leathers, where paleness of tint is important. It is difficult
to make a second extraction of tannin in the case of the natural
material, as, after the first extraction, it forms a soft pulp,
through which water will not easily percolate.

HEMLOCK (_abies canadiensis_) is an important tanning material, both
the bark and the wood being extensively used in America. The wood is
now generally converted into extracts in factories built near the
principal forests. Of late years, this extract has been imported into
the United Kingdom in fairly large quantities, in order to produce a
cheap red sole leather to compete with the American hemlock-tanned
leather. It contains only about 25 per cent. of tannin, but its value
is increased by its contents of insoluble non-tannins, which give
weight and solidity to the leather. Hemlock really gives a strong,
durable leather, but in America the practice of using artificial
weighing materials, such as glucose and Epsom salts, with a reduced
quantity of tanning material, has considerably lowered the value of
this leather.

In addition to the materials described, there are several of minor
importance which can only be briefly mentioned.

LARCH BARK is obtained from the tree _larix Europea_, which is found
in Scotland and North Europe. It contains 10-12 per cent. of tannin,
which gives a light colour and pleasant odour to leather. Scotch
basils (sheep skins) are tanned with this bark.

BIRCH BARK, from the white birch, _betula alba_, is another aromatic
tanning material. It contains only about 5 per cent. of tannin,
and is, therefore, generally used with other tanning materials.
It contains a tar which imparts an agreeable scent to the leather
that protects it from the ravages of insects. In conjunction with
willow bark (_salix arenaria_) it is used in the tanning process
for the real Russia leather. An oil containing the scent can be
extracted from the birch bark by dry distillation, and this extract
is sometimes used during the dyeing process, in the manufacture of
imitation Russia leather, which, however, only retains the scent for
a few months, whereas the real Russia leather has a permanent odour.

CANAIGRE (_rumex hymenosepalum_) is the tuberous root of a dock
plant indigenous to Mexico and the Southern States of America. It is
fairly rich in tannin (25-30 per cent.) and yields a moderately firm
leather. It contains too large a proportion of starch, however, and
cannot be described as a really satisfactory tannin. Moreover, it is
not harvested economically and the only way to make a satisfactory
tannin of it is to convert it into extract and remove the starchy
matters near the source of supply, if anyone dare take the risk of
establishing a factory in Mexico.

BABLAH or BABOOL (_acacia arabica_ or _acacia vera_) grows in India,
Egypt, and the Sudan. The bark of the babool tree is one of the
principal tanning materials used in India for hides, calf, and sheep
skins, which are sent in large quantities to Great Britain in a
rough-tanned state and dressed there. It contains 15-20 per cent. of
tannin, which readily oxidises in the leather in contact with light,
turning into a bright pink colour. It also seems to weaken the fibres
of animal tissues, and, for that reason, babool-tanned leather was
condemned by the Society of Arts Commission on Bookbinding.

The pods contain from 20-30 per cent. of tannin and give a mellow and
plump leather similar to that produced by gambier. The bleaching of
the material is troublesome, and it is probable that its use would be
increased if the tannin were prepared in the form of extract.

CUTCH is a crude extract made from the Indian tree _acacia catechu_.
This is the real cutch, as distinguished from the mangrove "cutch."
It is very rich in tannin (50-60 per cent.), but contains a large
proportion of insoluble matter and is, therefore, very little used
for tanning. It is well adapted for the dyeing of dark colours or
black with mineral strikers, such as chrome and iron salts; but
its chief use is for tanning fishermen's nets, which it renders
waterproof.

Commercial tannic acid, used for medicinal purposes, is prepared from
galls or excrescences on oak trees growing in Asia Minor. These galls
are caused by an insect (_cynips_) puncturing the small branches
and producing abnormal growth in the perforated parts. The acid is
gallotannic, which, if used for making leather, would produce a soft,
spongy, and nearly white leather. This tanning material is used a
little by Near Eastern tanners, but the result is unsatisfactory.


CLASSIFICATION OF TANNING MATERIALS

Tanning materials are divided into two main classes: (1) Pyrogallol,
(2) Catechol. The pyrogallol tannins give a bluish-black colour,
and the catechol tannins a greenish-black, with iron salts. Bromine
water does not precipitate pyrogallols, but causes a precipitate with
catechols. Pyrogallols yield ellagic acid (called "bloom" in the
trade), which improves the waterproof qualities of leather. On the
other hand, catechols contain a large proportion of insoluble reds,
or phlobaphenes, which are deposited between the fibres and thus give
solidity to the leather. Pyrogallol tannins give a light coloured,
soft leather, and can be used alone satisfactorily; but heavy
leathers, such as sole and belting, need a blend of both kinds of
tannin. The pyrogallol tannins include sumach, chestnut, myrobalans,
divi-divi, oakwood, algarobilla, chestnut oak, willow, and galls.
The catechols include quebracho, gambier, hemlock, mimosa or wattle,
mangrove, larch, birch, canaigre, and cutch. Oak bark and valonia
contain some of the properties of both classes of tannins.

There are sub-divisions of these two classes, arranged according to
chemical tests, by which one tanning material can be distinguished
from another.


TANNING EXTRACTS

The manufacture of extracts from vegetable tanning materials has
increased so rapidly of late years that the process of tanning has
undergone radical changes; and, whereas the tanner was limited to
three or four materials thirty years ago, he now has the choice of
about twenty good materials. These tannins can be suitably blended
to produce first-class leather. The processes in extract manufacture
are few. The wood, bark, or fruit is broken up into small pieces
and macerated in hot or cold water. The concentration of the liquid
is done in vacuum, or in an evaporator. The latest method is to
treat the tan liquor in a "triple-effect" evaporator (Fig. 4),
the object of using three compartments being to economise in steam.
This apparatus makes liquid extracts; where a powdered or crystal
extract is required, the liquid is afterwards treated in a vacuum
drying apparatus. Some extracts contain a lot of colouring matter and
insoluble substances. To overcome this defect, they are clarified
with blood albumen, sulphites, casein, or acetate of lead.

  [Illustration: FIG. 4.--TRIPLE-EFFECT EVAPORATOR (Blair, Campbell
  & McLean, Ltd.)]

SYNTHETIC TANNINS

The discovery of a synthetic tannin, in 1911, by Dr. Stiasny, who
was then an assistant in the Leather Industries Department of Leeds
University, created a great deal of interest in the leather trade,
and can certainly be regarded as a triumph of the application of
chemistry to industry. It was thought at first that these tannins
might play as important a part in the leather trade as the synthetic
dye-stuffs have, but it is now generally believed that this will
not be the case. Their use is likely to be as an aid to tanning,
rather than as a complete tanning agent, although it has been found
practicable to use them for one or two classes of light skins, where
it is essential that the colour of the leather should be nearly white.

The original patent was taken out in September, 1911, in Austria,
the native country of the inventor, but the patent rights have also
been protected in other countries, while the manufacture and sale of
the product passed into the hands of a large German dye firm, who
have since taken out several patents for other synthetic tannins.
The original tannin is produced by treating a sulphonated phenol
with formaldehyde. A patent had been taken out several years before
for the use of formaldehyde in tanning, but this expired early in
1911; many patents had also been granted for sulphonated phenol
preparations, chiefly as disinfectants, but it was left to Dr.
Stiasny to discover the value of combining the two chemicals by the
process of condensation. The preparation, first known as "neradol,"
is now made in England under licence, but, since the war, its cost
has been more than doubled, so that it is unlikely to replace natural
tanning materials to any great extent.

Formaldehyde itself has certain properties which are harmful to
leather, and it must be used with extreme caution and in small
quantities to avoid these defects. It is used in the leather trade
chiefly for keeping up the substance of hides during the tanning
process, and thus causing a rapid absorption of tannin. At the
beginning of the tanning process, the liquors are acidified,
preferably with a weak organic acid, which causes the fibres of
the hides to distend. It is at this stage that the formaldehyde is
used. This method, which cannot improve, but may easily damage, the
leather, is almost entirely confined to the Continent. Formaldehyde
has a hardening and tanning effect on animal tissues, and leather
treated by this process often has inferior wearing qualities.

In the case of the artificial tannin, this property of formaldehyde
is to a large extent modified by the chemical reaction with a
sulphonated phenol, the addition of which also increases its tanning
effect; but, while the tannage is very rapid, especially in the case
of light skins, leather produced solely by means of artificial tannin
has a slight tendency to dryness after being in stock for some time.

No doubt, however, methods will be found to overcome initial
difficulties, and various liquors will be prepared to meet different
requirements. The question of price remains the deciding factor as
to its use on an extensive scale, for, while it is so high, natural
tanning materials will be preferred, except in a few special cases.
According to the hide-powder method of tannin analysis, Neradol
contains about 30 per cent. of tannin, but there are many natural
tannin extracts containing nearly double the amount of tannin at
nearly half the price of the artificial tannin; the latter, however,
has a more rapid action and also produces a nearly white leather.
Another advantage of Neradol is that it prevents drawn grain, so
that, if raw hides be treated with a small quantity before tanning,
stronger vegetable tan liquors may be safely used to hasten the
process. In the manufacture of sole leather, for example, limed
hides, after washing in water, may be suspended in a solution of
Neradol containing 3 to 5 lb. per 100 gal. of water for twelve to
twenty-four hours. This quantity produces a slight tanning effect,
the hides are thoroughly delimed, and strong vegetable tan liquors
may then be used to complete the tannage without the grain of the
hide being drawn or dark in colour, as would be the case if the hides
were not first treated with the artificial tannin.

Neradol is also said to be an effective bleaching agent for tanned
leather in a 5 per cent. solution for a few hours, without any loss
of weight.

This property may also be utilised in the production of chrome
leather, where a whiter colour is required than that produced by
the ordinary chrome tannage. For this purpose it may be used in a
pickling liquor before the one-bath process, or in the second bath of
the two-bath tannage.

For dressing wool and fur skins, the synthetic tannins are much
superior to the alum and salt process.



CHAPTER IV

LEATHER WORKING MACHINERY


When it is considered that the construction of machinery for the
leather trade had barely started thirty years ago, the wonderful
variety and utility of modern machines are remarkable, and it is a
moot point whether engineering science has not played as great a part
as, or even greater than, applied chemistry.

Excepting the bark mill, various kinds of tumblers, the fulling
stocks, glazing and rolling machines, there were practically no
efficient mechanical aids to lighten the exceedingly laborious
operations incidental to leather manufacture two decades ago; but
so many improvements have lately been made in the construction of
machinery for practically every operation in the trade that most
of the machines require very little skill to work them, and can be
operated by intelligent youths after a few weeks' experience.

The change has been of great benefit to the health of the workers,
for the continual stooping over beams and sloping tables, combined
with the arduous nature of the work, was very injurious. The
reputation that tanning had as a healthy occupation was due more
to the work of the labourers than that of the skin workers. (The
old-fashioned lime-yards and tan-yards were generally in the open,
whereas modern tanneries are roofed.)

Leather trades machinery was not a success at first, probably because
it was very difficult to get the necessary information from leather
manufacturers. However, as the engineers gained more experience of
the methods of leather-making, the defects were gradually remedied
until it may be truly said that the machines now reach a high state
of perfection. It was no uncommon thing for workmen to lose a finger
or two in a machine, but such accidents are now rare, owing to
improvements in the construction of the machines.

Most of the machines used in the leather trade are of the cylinder
type, the raw skins or leather passing between two rollers, of which
the upper one performs the operation while the lower one helps to
draw the material through the machine. To prevent accidents and
control the working of machines, a third roller is often used, which
serves to "feed" the leather or skins to the working cylinders. Of
this type of safety roller, the Seymour-Jones attachment to the
shaving and buffing machine is of great importance.

  [Illustration: FIG. 5

  SHAVING CYLINDER]

The operations of the tannery, which are performed by cylindrical
machines, are dehairing, fleshing, scudding, samming, shaving,
scouring, striking-out, setting, boarding, buffing, graining,
printing, embossing, and blacking or colouring. The working cylinders
usually vary according to the character of the operation, although
one or two types may be used for at least three different operations.

Where cutting or paring is done, the working cylinder is fitted with
brass blades, or steel blades backed with iron. The blades are spiral
in some machines, and are so arranged that half of them converge to
the left, and half to the right (Fig. 5). When in work, this type of
cylinder not only performs the operation for which it is specially
intended, but also stretches the leather outward, by reason of the
arrangement of the blades or knives. The blades overlap one another
to obviate marking, for if the blades met exactly at the centre they
would make a line on the leather. Figure 6 shows another arrangement
of knives for the process of buffing.

  [Illustration: FIG. 6

  BLADED CYLINDER FOR "BUFFING" LEATHER]

  [Illustration: FIG. 7

  BAND-KNIFE SPLITTING MACHINE]

The most important machines outside the working cylinder type are
the splitter, and the glazer. There are several kinds of splitting
machines, but the band-knife machine (Fig. 7) is the most largely
used. This is a veritable triumph of the engineer's art, for it
is possible to make five or six layers, all about the same size,
out of one hide, although leather is only split once or twice as a
rule. Of course, sole, belting, and other thick leathers are not
usually split. The invention of the belt-knife splitting machine
revolutionised the leather trade, and there would undoubtedly have
been a great shortage of leather without it. Formerly, all the
levelling and reducing of substance was done by paring off quite
small pieces with the shaving knife (Fig. 8), a difficult and
laborious work. These parings were only suitable for pulping and
compressing into leather board; but now the flesh splits removed
by the machine can be curried, enamelled, printed, or rolled to
make serviceable leathers, although, of course, not nearly so good
in quality as the top or grain split. The main working part of the
splitting machine is an endless steel knife which passes round two
wheels placed at opposite ends of the machine. The leather is drawn
to the knife through two rollers, of which the lower one is in
sections to allow very thick parts of the hide to pass through the
machine. It would need a large volume to describe in detail all the
different machines used in the leather trade; the constructional
details of only one machine can be given, and, in view of its
importance, the shaver is selected. Reproductions of other machines
will appear in succeeding chapters.

  [Illustration: FIG. 8

  SHAVING KNIFE]

Nearly every leather trades' engineer constructs shaving machines,
but the Howard-Smith is described here, not because it is the most
popular (unfortunately there is a decided preference for low-priced
machines), but because it is one of the best from an engineering
point of view, and because several improvements are embodied in its
construction.

  [Illustration: FIG. 9

  SHAVING LEATHER

  (Old method)]

This machine consists of nearly one hundred parts and each is made
of the best material available. The advantage of this is obvious when
the question of repairs is fully considered. The first Howard-Smith
machine made has been running more than four years, and has not
cost the owner a penny for repairs, beyond, of course, the expense
of replacing the blades of the working cylinders; whereas it is no
uncommon occurrence for a cheap machine to be thrown on the scrap
heap after a few years' wear. It is always advisable, therefore, to
buy machinery of the best grade.

  [Illustration: FIG. 10

  DRAWING OF SHAVING MACHINE]

Figure 10 represents a drawing of the shaving machine, _A_ being the
side view, and _B_ the front. The work of the draughtsman generally
appears to the uninitiated to border on the miraculous; he is often
the designer and architect of the machine, and his work is certainly
interesting and skilful.

Many of the heavy parts, such as main castings, pedestals, etc.,
are made in the foundry, which may be part of the leather trades'
engineer's works if he is in a large way of business. The finer
parts, those which might be termed the fittings, are made in the
turnery department; while the machine is assembled in the fitters'
shop.

Figure 10 _A_ shows the side, and 10 _B_ the front construction of
the shaving machine. The figures indicate, by following the arrows,
the principal parts of the machine, which are shown in detail in
sectional tracings. For example, _T._ 65, of which no working parts
are shown in the diagram of the complete machine, is reproduced in
detail in a separate drawing shown in Figure 11. Each part of the
machine is numbered and entered in a stock-book.

In describing the principal parts indicated in Figure 10, it will
give an idea of the assembling of the machine if a beginning be made
with the main iron castings. These comprise the main bed (64), two
side frames (62), and the front frame (58). The side frames are
strengthened by the ribs which form the edge, and which are about
three times as thick as the body of the casting. The object of the
front frame is to support the foot lever (59), the rocking frame (57)
carrying the rubber roll (79), and the wooden roof (75) over which
the leather is passed. The spring (76) pulls back the rocking frame
(57) when relieved by the operator removing his foot from the lever
(59). The long spring (77) lifts up the foot lever (59) when the
latter is released.

The pullies (73) are connected with the knife cylinder which shaves
the leather. The cylinder is obscured by the wheel-guard (65) and is,
therefore, shown separately. This cylinder is comprised of a shaped
piece of steel (turned out of solid metal bars of 4-3/4 in. diameter)
into which spiral steel blades are caulked with copper or brass.
When turned, the body of the cylinder is 4-5/8 in. in diameter, but
the parts forming the bearings are reduced to 1-1/2 in. The number
of blades is twelve, fourteen, or sixteen, according to the kind of
leather shaved, and to the choice of the operator.

It is interesting to note that these blades are now being made in
Sheffield, although, before the war, they had to be imported. The
knife guard (65), shown in detail in Figure 11, is an ingenious
contrivance which prevents the operator's hands being drawn into the
machine. It consists of an automatic shutter worked by a steel chain
from the foot lever. Figure 11 _a_ represents the shutter closed down
on the knife with the rubber roll, on which the leather is carried to
the knife, at a safe distance from the shutters. Fig. 11 _b_ shows
the position when the machine is shaving the leather, the guard being
clear and the rubber roll engaged with the knife.

  [Illustration: FIG. 11 _a_.]

  [Illustration: FIG. 11 _b_.]

In order to sharpen the blades of the cylinder, a carborundum wheel
is fixed in close proximity, its position being indicated in the
drawing by the wheel cover (67). A bracket for feeding the wheel
to the blades when grinding them is shown at 66. When grinding the
blades, the saddle (68) carries the wheel backwards and forwards
across them. A special feature of the saddle in this particular
machine is the double-thread screw, one a right hand, and the other
a left hand. The saddle (68) is actuated by a "swimmer," as the
makers term it, which engages, say, first the right-hand thread; when
the saddle has travelled to the end of its movement the "swimmer"
automatically enters the left-hand thread, and the saddle is
rotated in the opposite direction. The "swimmer" can be disengaged
instantaneously. A brush (55) is fixed near the cylinder to remove
any leather shavings adhering to the blades. It also acts to some
extent as a fan, and, by creating a current of air, carries the
leather dust away from the operator. A trough is filled with water
to catch the dust from the carborundum wheel, while the knives are
being ground. The trough should be cleared out and refilled with
clean water from time to time. It is essential that no dust from
the grinding wheel comes into contact with vegetable tanned leather
required in a natural or colour finish, otherwise it will cause iron
stains, which are difficult to remove without damaging the leather.
For this reason, the knives should not be ground while this class of
leather is being shaved.

An important detail of the machine under description is a trueing
device. Knives are often roughened owing to the carborundum wheel
wearing irregularly. The trueing device keeps the wheel perfectly
true by means of a diamond held in the end of a screw (78). Another
ingenious arrangement (patented) is a spring (79_a_) placed at the
back of the rubber roll (79), which enables the roll to spring back
when the leather, or any part of it, is too thick for the cutting
cylinder.

A unique advantage of the Howard-Smith machine is that it is
ball-bearing throughout. The main driving shaft revolves on four
massive ball-bearings in case (71). The pullies are firmly fixed
to the driving shaft with keys or feathers. Afterwards the pullies
are machined, so that the whole shaft with its pullies is perfectly
balanced, and the machine runs smoothly without vibration.

The bladed cylinder is likewise mounted on four ball-bearings.
The intermediate driving shaft (70), which is mounted on two
ball-bearings, is connected with a large drum shaft (70_a_) which, in
its turn, sets the carborundum wheel in motion.

  [Illustration: FIG. 12

  SHAVING-MACHINE

  (Haley)]

Fig. 12 represents another make of shaving machine.



CHAPTER V

PREPARATION OF HIDES AND SKINS FOR TANNING


Before beginning a description of manufacturing processes, a precise
definition of leather may be given. Laymen usually describe leather
as "hides tanned with bark," Since the introduction of modern
processes, however, this is only partly true. In any case, the
definition is very broad.

The primary objects of treating raw hides and skins to produce
leather is to make them imputrescible and impart various degrees
of pliability. These qualities are essential, but the simpler the
methods used to attain them, the greater the strength of the leather
produced.

The number of materials that will produce leather is legion. Whereas
oak bark was almost exclusively used for tanning until the last
century, there are now at least twenty useful vegetable tanning
materials. The active ingredient of all of these materials is tannin,
a colloidal or uncrystallisable substance. Correctly speaking, the
term "tanning," used to designate the process of converting hides
into leather, should be confined to the use of vegetable tannins;
unfortunately, the trade has largely adopted the word in many other
processes of making leather. For example, large quantities of leather
are produced by the use of minerals, and especially of chrome salts;
where the latter is used, the leather is said to be "chrome-tanned,"
although "chromed" would be a more accurate definition. One mineral
process of making leather, namely, that involving the use of alum,
or alumina sulphate, and salt, is technically described as "tawing,"
The conversion of skins into leather by the use of oxidised oil is
known as "chamoising," imitation chamois leather being made by that
process. Nearly every mineral has the property of converting skins
into leather, though most of them are of little practical value.
The most successful are the chrome salts, and alum and salt. The
use of iron salts would be by far the cheapest process, if means
could be found whereby they could be successfully used. Sixty years
ago, a chemist named Knapp experimented with iron salts, but failed
to produce satisfactory leather. Patents were taken out in Austria
in the early part of 1914 for the use of iron salts in tanning,
while a patent of more recent date covers the use of iron salts
in combination with chrome salts. Neither of these appears to be
of much practical value. The cheapest and most stable iron salts,
the sulphate and chloride, have strongly acidic properties, and,
therefore, have a somewhat destructive and hardening effect on
animal fibres. The iron salt that might convert skins into leather
is the carbonate, which is difficult to prepare cheaply enough for
commercial purposes, though it is used medicinally. A basic iron salt
might also be useful, but iron tannages would only be suitable for
black leather. Oils and fats also have leather-making properties,
fish oils being used for the manufacture of "chamois" and antelope
leather. There are other methods of producing leather which are
not used on a large scale, but sufficient examples have been given
to show that an exact definition of leather cannot be summed up in
one or two words. There are now many kinds of leather produced by
varying methods, and each class requires its own definition. Broadly
speaking, however, leather is an imputrescible material produced from
the raw skins of animals, chiefly of cattle, sheep, and goats, by
treating them with tannins extracted from the barks, wood, fruit, or
leaves of trees; or with chemicals (chiefly chrome salts, or alum and
common salt); or with oils and fats.

The preliminary processes are of great importance, as they determine
to a large extent the character of the finished leather. Mistakes
made in the early processes can never be effectually remedied.

The first operation is technically known as soaking, and its object
is to cleanse the hides or skins thoroughly. This is quite simple
in the case of raw hides received direct from the slaughterhouse,
as it is merely a question of soaking them in clean, soft water for
a few hours. If the only water available is hard, 1/2 lb. of borax
should be added for every 100 lb. of raw hides. Borax is useful in
any case, as it is a splendid cleanser and a very useful chemical in
the tannery. Most of the hides used in the United Kingdom, however,
are wet-salted (_i.e._, salted in the wet state), as it has become
customary for most butchers to send hides and skins to the auction
markets in all the principal towns, where they are offered for
sale every week. It is still a debatable point among tanners as to
whether it is better to buy hides direct from the butcher or through
these markets. It is certainly a great advantage to put hides into
work quickly (although not before they are quite cool), as time is
saved in the soaking process, and there is practically no loss of
gelatinous matter. On the other hand, the tanner is able to buy just
the selection of hides that he wants from the auction markets. Under
this arrangement, several days must elapse before the tanner receives
them, and it is, therefore, absolutely necessary to preserve them,
otherwise they begin to decompose quickly. The first sign of decay is
the slipping of the hair, which, in that condition, may be pulled out
of its roots quite easily. Micro-organisms multiply rapidly in the
gelatine of the hide, the grain comes away, and decomposition sets in
so quickly that, in a few days after the removal of the hide from the
carcase, it may lose nearly half its value for tanning purposes if it
has not been preserved by salting or by drying rapidly in the shade
in a current of air. Salted hides need a more prolonged soaking than
fresh hides, as it is essential that all trace of salt be removed
before the next process, otherwise the finished leather may be flat,
and poor in quality. Usually, two days' soaking in several changes of
water is necessary. For the soaking process, fresh or salted hides
and skins are either soaked in square, cement-lined, brick pits, or
in wooden vats filled with clean, cold water. A good system is to put
a pack of skins in one huge tank filled with clean water and leave
them in soak overnight before transferring them to the ordinary pits.
Each pit will take 50 hides, or 10 dozen calf skins, or 20 dozen goat
skins. Tanners designate as a "pack" each lot of hides or skins they
work through, irrespective of the quantity.

  [Illustration: FIG. 13

  DRUM TUMBLER]

  [Illustration: FIG. 14

  FALLER STOCKS]

Besides salting them, there are other ways of curing hides and
skins, and a large proportion is simply dried or dry-salted, the
salt in the latter method being applied while the hides are moist.
Dry hides, whether "flint" (i.e., simply dried) or salted, require
special treatment to make them soft and pliable, without which it
would be impossible to convert them into leather. Soaking in plain
water is insufficient, as it would need too much time, during which
there would be a great loss of gelatine. The use of chemicals and
mechanical motion are required; sometimes chemicals alone will
thoroughly soften the hides, but this is not often the case. Both
alkalies and acids may be used for softening dried hides, and it
is difficult to say which gives the better result, although the
former are frequently used, mainly because treatment with acids is
a comparatively recent innovation. Both kinds are effective, but
the use of acids retards the loosening of the hair, although it has
been proved experimentally that acid-softened hides give a slightly
improved yield of leather compared with the effect of the alkaline
process--a noteworthy advantage where the finished leather is to
be sold by weight. The acid generally used--formic--has antiseptic
properties, and can have no harmful effect on animal tissues, as is
generally the case where mineral acids, especially sulphuric, are
used. Sulphurous acid is also said to be a good softening agent for
hides, but it is rarely used. The most satisfactory alkalies are
sulphide of sodium (crystallised or concentrated) and caustic soda,
and of these two, the sulphide is preferred in nine cases out of ten.
The quantities used vary according to the condition of the hides, but
the average is about 1 lb. of caustic soda, or 1 lb. of concentrated
sulphide of sodium (65 per cent.), or 2 lb. of crystallised sulphide
of sodium (30 per cent.) for every 100 gal. of water. Of formic
acid, 1 lb. is sufficient for 100 gal. of water. It is possible to
soften hides by these means without mechanical acid, but the time
is considerably shortened by "drumming" the hides, _i.e._, placing
them in a round or, preferably, a square tumbler fitted inside with
shelves or staves (Fig. 13). The drum is rotated mechanically for a
few hours, during which time the hides are thoroughly kneaded and
softened by the alkali. Tanners often use a machine known as the
"faller stocks" (Fig. 14), which kneads the hides very thoroughly,
though somewhat drastically. The drum method is preferable, providing
the hides can be suitably softened. An old method, and one that is
used now by some of the small firms, is to "break over" (_i.e._,
vigorously scrape) the hides with a curved blunt knife fitted into
two wooden handles. For this manual operation, the hide is placed,
flesh side up, over the tanner's beam (Fig. 15) and is then scraped
with the knife.

  [Illustration: FIG. 15

  TANNER'S BEAM]

Another old method, which has not yet disappeared, is to make use of
stale soak liquors, which, although efficient for softening purposes,
cause a great loss of hide substance owing to the active growth of
bacteria, which are developed as a result of the water becoming foul
and putrid with dirt, blood, and dissolved gelatinous matter. This
method of soaking is always dangerous, apart from the great loss of
gelatine, for the thin grain (hyaline layer) is liable to be eaten
away in patches, a defect which greatly reduces the value of leather.

Dried hides are not only difficult to treat successfully in the
different processes of making them into leather, but they are also
of highly speculative value, although they are well preserved when
completely dry. It sometimes happens, however, that the drying
is imperfect; it may, for example, have been so rapid that the
exterior of both sides is thoroughly dried before the air is able to
penetrate into the centre. The result is that the interior of the
hide putrefies, but there may be no indication of this until the
hides are soaked and softened, when they may fall to pieces and are
only saleable to glue makers. Again, the hides may be dried in the
hot sun and be badly blistered, with the same result as regards their
value for leather. If the hides are dried in too high a temperature,
they become horny and rarely make satisfactory leather owing to the
difficulty of softening them. It is estimated that quite 10 per
cent. of the dried hides are improperly cured and, therefore, useless
for making into satisfactory leather.

Apart from the commercial risk in buying dry hides, their import,
especially from Russia and China, is a source of danger in conveying
the disease of anthrax to workmen. It has been conclusively proved
that dried hides are much more liable than wet-salted hides to cause
infection.

So far, only one country, the United States of America, has taken
steps to prevent the importation of the disease of anthrax, although
most countries have issued regulations in regard to the precaution
to be taken to avoid infection by anthrax in those factories where
imported hides, wool, hair, and bones are treated. It would seem
that the most rational method would be to disinfect the hides before
they are shipped, as it certainly appears to be unwise to import any
form of disease; unfortunately, the first regulations issued by the
American Government proved to be impracticable, as the suggested
method had the effect of lowering the quality of the hides, and
making the preliminary operations troublesome. Their second scheme,
consisting of baling a certain number of hides in canvas disinfected
with a 0.02 per cent. solution of mercuric chloride, is more
satisfactory, for, although it may not sterilise all the anthrax
spores inside the bale, it should prevent them reaching other goods.
This Government order only applies to hides, skins, hair, and wool
coming from countries where anthrax is known to be prevalent.

The disease of anthrax is generally contracted by workers through
sores or cuts in the hand; the bacilli multiply rapidly in contact
with the blood, and the first sign of disease is usually shown by
a red swelling or pimple in the neck. If treated at this stage by
anti-anthrax serum a cure is often effected, but if treatment is
delayed the disease quickly proves fatal, the patient dying in awful
agony. The germs of the disease may also be swallowed and the disease
develop internally, but cases of this kind are rare.

Besides the danger to workers, there is the risk of cattle being
infected. The effluent from tanneries where anthrax-infected skins
are treated contains millions of bacilli, and it is doubtful if the
latter are sterilised even when the effluents are precipitated and
aërated before they are run into streams or municipal sewers. In any
case, the sediment may be infected, and this ultimately finds its way
to the land.

Until the various European Governments insist on imported hides
from anthrax-infected areas being sterilised before shipment, the
use of a disinfectant such as lysol or a similar cresylic compound,
or bichloride of mercury, seems imperative in the first process of
soaking. The use of these disinfectants would make the waste liquors
fit for discharge into sewers or streams.

The English Public Health and River Pollution Acts have had a great
effect in improving the hygiene of the tannery, although leather
manufacturers have not welcomed them, as, in some cases, they have
meant considerable expense in providing settling tanks for the
treatment of waste liquors. The Public Health Act gives power to any
town corporation to declare as offensive trades such businesses as
tanning, hide and skin merchanting, fellmongering, tallow melting,
etc., and several boroughs have taken advantage of this law. In such
cases, anyone desiring to set up business in these trades must apply
to the Town Council, who may or may not give their consent; in fact,
a few applications to establish these businesses have lately been
refused.

While the curing of wet hides with salt or in brine is more
satisfactory than drying them, the use of ordinary salt is not an
ideal method, as 10 per cent. brine dissolves hide substance. The
recent introduction of a pure dry salt (99-98 per cent.) and of a
sterilised salt for commercial purposes has to a large extent removed
the objections to ordinary salt. Dry sulphate of soda is also a
satisfactory cure. It may be that, as hygienic conditions are further
advanced in the various industries, a suitable disinfectant will have
to be used for all hides, in addition to the salt, except where the
hides are sent direct to the tannery from the slaughterhouse.

The cure of hides in hot countries, especially where cheap salt is
unavailable, is often unsatisfactory. A method of obviating this
difficulty has been found in China, where, in one or two of the
principal towns, hides and skins are preserved by freezing them in
cold-storage. Although this process stiffens the hides, it is said to
be fairly satisfactory if they are allowed to soften naturally before
soaking them. If submitted to rough treatment before the stiffness
relaxes, there is a great danger of the hide fibres being ruptured.
Freezing removes the difficulty of softening which is experienced in
treating dried hides, while it preserves the hide substance.

After the operation of soaking, hides and skins are ready to be
treated for the removal of the hair. There are several ways of
loosening the hair sheaths, but most of them consist of treating
the hides in a solution of a caustic alkali. The use of a solution
of common lime was practically universal until a few years ago, but
nowadays sulphide of sodium, red arsenic sulphide (realgar), and
caustic soda are also used, generally in admixture with the lime.
Another process consists in sweating the hides in a heated room,
preferably a damp cellar, where rapid decomposition of the hides soon
loosens the hair.

This method is rarely used in England, but a few American tanners
seem to prefer it for certain classes of hides. In the American
process, the hides are first soaked, and then cut in half down the
back, forming what are known as sides. Dry hides are subjected to
the usual mechanical operations in the faller stocks, in which they
are kneaded by two large hammers (Fig. 14), or they are drummed in
the tumbler (Fig. 13). After the sides are thoroughly softened and
drained, they are transferred to the sweat pit, which is, preferably,
a dark underground chamber. The stock requires very careful attention
as the process is risky. The temperature should never exceed 75° F.,
otherwise the hides may be irretrievably ruined. The process may take
from one to four days, according to the varying conditions of the
hides and of the weather. The loss of nitrogenous matter gives rise
to the development of a strong odour of ammonia, which is sometimes
even too pungent for the workmen. When the hair is judged to be
sufficiently loose, the sides are washed in cold water and put in
the stocks again for about ten minutes, when all the hair will be
removed; or the hair may be scraped off in the unhairing machine.
This method is not useful for sole leather, as it causes too great
a loss of gelatine, but it saves time in the production of sides
intended for boot upper leather, which is usually sold by measurement
(superficial area).

A dehairing process has lately been invented and patented, however,
which may supersede all of the methods just described. This process
consists in treating the hides with various enzymes which loosen the
hair so effectively that it can be removed more easily than the hair
of a limed hide. The fine, short hairs underneath are also removed,
whereas by the lime method a further process is needed to get rid of
these hairs. The only drawback to its use is that the inventor has
not yet been able to produce a material cheap enough to place on the
market, but as soon as this difficulty is overcome the enzyme method
may become fairly general. Neither the hair nor the gelatine of the
hide can be damaged by this method.

  [Illustration: FIG. 16

  LIME YARD

  ("Dri-ped" Tannery)]

The usual method of liming is carried out in brick pits of square
or rectangular shape with a sloping front on which the hides or
skins can be piled to drain (Fig. 16). There is a great variation in
the quality of lime, and in all cases it should be tested for the
available percentage of caustic lime. A good sample should contain
between 70 and 80 per cent. of pure lime. Buxton lime, which can be
obtained in powdered form, is particularly suitable for the tannery.
The ordinary lime is preferable to the chalk lime, as it is usually
stronger, though it sometimes contains more impurities. Gas lime is
the poorest of all. Lime should be stored in a dark place, otherwise
the outside of the heap carbonates quickly, forming chalk (CaO +
CO_{2} = CaCO_{3}) which is of no use for the liming process.

To prepare the lime for the pits it is slaked (_i.e._, formed into a
paste with water. All the lumps should be reduced to paste in order
to avoid lime burns, which are caused by direct contact of the hides
with pieces of unslaked lime. A certain quantity of the paste is then
added to the water or old lime liquor in the pit, and the liquor is
well plunged up to hasten solution and diffusion of the lime. A long
wooden pole, with a flat block of wood attached, is used for this
purpose and also for pressing down the hides under the surface of the
liquor.

Two methods of liming are in vogue: (1) the single-pit system, and
(2) the three-pit system; but the latter is the better method, as
it is more easily controlled, and causes less loss of gelatine than
the former. In this system the liquor is strengthened with fresh
lime for each pack of skins. Its great fault is that the pit is
only cleared out at long intervals in order to take advantage of
the mellowness of used lime liquors; hence, there is frequently
large accumulation of insoluble limestone and other sediment from
the lime, in addition to a quantity of dissolved gelatine, which
rapidly accumulates putrefactive bacteria. When the pit is cleared
out the process of liming is disturbed for a time, as fresh lime
liquors are not beneficial to hides and skins, and the loosening of
the hair is delayed. On the other hand, the three-pit system permits
liquors of uniform strength, and the process is continued without
interruption. Each new pack is first placed in the oldest of the
three liquors, which is then cleared out, and a new liquor prepared.
From the weakest pit the hides pass to a stronger liquor, and the
process is finished in the third pit, which should contain a new lime
liquor. The mellow liquors, being charged with bacteria, facilitate
the loosening of the hair, while the third liquor, consisting of
fresh lime, serves to swell the fibres of the hide, by means of which
the flesh is more effectually removed. The lime also forms a soap
with the natural grease of the hide; this grease can therefore be
removed. In some cases, however, especially in the cattle fed up for
Christmas, the hides contain a larger quantity of fat than the alkali
of the lime liquor can convert into a soap, and the surplus grease is
frequently seen in the finished leather, as it is difficult to remove
in later processes. A solution of hyposulphite of soda, or lactic
acid, given just before the process of tanning is said to remove the
grease, although a slight loss results in the case of those leathers
sold by weight. The objection to natural grease in leather can be
understood where the latter is intended for colours, but in the case
of sole leather it ought not to be a disadvantage, yet, owing merely
to the darker appearance of the leather where the grease reaches the
grain, its selling value is reduced by 2d. or 3d. per lb. The strange
part is that the grain of this sole leather, when made into boots, is
buffed on an emery wheel, then sometimes coloured with a paint, and
finally sold in boots at the same price as leather free from grease
and regular in colour.

The liming process in pits takes from six days to a month, according
to the character of the leather required. Light calf skins may
be ready for unhairing within a week, while hides intended to be
finished for "raw hide leather" may be left in the pits quite a
month, the object being to distend and harden the fibres. Lamb
skins intended for parchment, and small calf skins for vellum, are
also subjected to prolonged liming. Between these extremes, there
are several stages in the process which have varying effects on the
character of the finished leather. In fact, it is a tanner's dictum
that leather is made or marred in the lime liquor, though this, of
course, only applies to a certain extent. Generally, however, the
heavier the hides, the longer the liming required. Fortunately,
the limited solubility of the lime in water affords a wide margin
of safety in working, and the only danger to guard against is the
too prolonged use of old liquors, which are readily detected by the
strong odour of ammonia. One important property of lime is its lower
solubility in hot than in cold water.

Lime by itself does not readily attack the hair bulbs, and the
slowness of the process has led to the introduction of other
chemicals, generally for use in conjunction with lime. The principal
of these are sulphide of sodium and red arsenic. Mixtures of sulphide
of sodium and lime, or red arsenic and lime are now largely used,
the former for hides, calf, and sheep skins, and the latter for
goat and kid skins. Both sulphide of sodium and arsenic dissolve
keratinous matters (horns, hair, etc.) and workmen should, therefore,
be provided with rubber gloves to prevent the loss of their finger
nails. Sulphides naturally lower the commercial value of the hair
removed and, if used alone, destroy it. In admixture, however, the
hair has some value, although it is not so good as that removed by
the use of pure lime. Against this, however, there is a great saving
of time and less loss of hide substance and, therefore, increased
weight of leather. Sulphide of sodium is prepared in crystallised
or concentrated form; the former, about 30 per cent. strength,
is preferred in Great Britain, while the latter--65 per cent.
strength--is prepared for export, the main object being to save the
cost of transit of 35 per cent. of water. About thirty different
sulphide salts may be used, but the sodium and arsenic disulphides
are the best, as it has been shown that the most rapid loosening of
the hair occurs where the quantities of sulphur and alkali are nearly
the same. There are two arsenic salts used in the trade, namely,
realgar, or red sulphide of arsenic (As_{2}S_{2}) and orpiment, or
the yellow sulphide (As_{2}S_{3}), but the former is often preferred
as it is said to give better results than the latter. In practice,
the proportion of arsenic used is 1 part in 20 parts of lime,
although it naturally varies a little according to the class of skin
under treatment. Sulphide of sodium is used in the proportion of 1
part to 10 of lime, or, if concentrated sulphide be used, 1 in 20.
The quantities of lime, or lime and sulphide, used are estimated on
the weight of the raw hides. For hides intended for sole leather, 5
per cent. of lime on the weight of hides is ample, while a little
more may be used for hides intended for dressing leather (_i.e._,
leather which has to be dressed or finished with a certain degree of
flexibility for bags, boot uppers, etc.). When a mixture of lime and
sulphide is used, 3 per cent. and 0.3 per cent. respectively is a
satisfactory quantity. The action of this mixture on hides is complex
and has not yet been definitely ascertained, but it is thought that
the calcium sulphydrate formed by the chemical reaction between
sulphide of sodium and calcium hydrate (slaked lime) is the active
principle.

In the pit method of liming, it is essential that the liquors be
frequently plunged, while the hides should be taken out ("hauled"),
piled to drain for a few hours, and put back again ("set"), or
transferred to another pit. Although lime is more soluble in cold
than in warm water, it is found in practice that the process may
be stopped or considerably retarded in very cold weather, and the
activity of the liquors is increased by the application of waste
steam (conveyed through iron pipes from the boiler).

Sulphide of sodium and lime are sometimes made into a thin paste,
which is applied to the hair side of hides and skins with a mop or
fibre brush. The hides are then folded down the back with the flesh
sides out; other hides are similarly treated and placed in a pile.
This saves a great amount of labour in pitting, and, if the paste is
fairly strong, consisting of 2 to 2-1/2 per cent. sulphide, the hair
can be removed after a few hours.

With so many depilatories available, it is not surprising that
several patents have been granted and numerous suggestions made with
the object of trying to improve on the old process of liming. While
there may be some objections to lime, it has a few advantages which
are lacking in other depilatories. These advantages are not perfectly
understood theoretically, but the tanner recognises them in practice.
Hence, there are very few tanneries where lime is not used at all,
and the only progress that seems to have been made in the process of
liming consists in the admixture of sulphide of sodium or arsenic to
hasten the process, reduce the loss of gelatine, and, in the case of
arsenic, to improve the fineness of the grain of skins for boot upper
and glove leathers.

One patented method consisted in forming the calcium hydrate within
the hide by treating it with a 1 per cent. solution of caustic soda
and then with a 1-1/2 per cent. solution of calcium chloride, the
reaction of these two chemicals forming calcium hydrate (lime) and
sodium chloride (salt). This method, however, does not loosen the
hair at all and has to be supplemented by soaking the hides in putrid
water. It is a good method of liming hides or skins dressed in the
hair, as it opens up the fibres without weakening the hair roots and
prepares the hides in a suitable condition for tanning.

Another method consists in mixing a small quantity of soda ash with
the lime, thereby hastening the process by increasing the alkalinity
of the liquor.

A somewhat complicated method was introduced a few years ago, but,
although it seemed advantageous from a chemical point of view, it
has not proved successful in practice so far as is known, probably
because of its expense. In consisted of four distinct processes. The
hides were first mopped on the hair side with a thin paste of lime
and arsenic, and dehaired after twenty-four hours. In the second
process, they were treated in a drum for twenty-four hours with a
solution of sodium sulphide, they were then drummed for twenty-four
hours in a solution of hyposulphite of soda, and finally placed in
a vat or pit containing a solution of lime and a little arsenic for
two to five days. After washing, etc., they were ready for tanning.
The sulphide of sodium swelled the hides or skins by distending
the fibres, and the natural fat is converted into a soluble soap.
The hyposulphite arrests the action of the sulphide and acts as an
antiseptic.

In modern yards it is a growing practice to use mechanical power to
keep the hides in motion, instead of handling them. The hides are
attached to poles joined to a strong cross beam, which, in its turn,
is connected by stout iron rods with the main pullies and shafting.
The installation is expensive, but it saves an enormous amount of
manual labour and time, while ensuring uniform treatment. This
method is not so much used for liming as for the tanning process.

After loosening the hair and opening up the fibres, the next
operation is dehairing or depilation, or, as it is generally
described in the trade, "unhairing." The hair must slip quite easily
before beginning this operation, otherwise a number of them will be
left in the hide and will be difficult, or almost impossible, to
remove later on if the hides are being made into sole leather. These
hairs present an unsightly appearance and lower the value of the
leather. Depilation may be done by hand or machine; but the latter
method is rapidly superseding the former, as it is in nearly every
other process of leather manufacture.

In the manual process, the hair is removed by scraping it off in a
downward direction with a blunt, convex-shaped knife, fitted into two
wooden handles (Fig. 17), the hides being placed on a sloping convex
beam (Fig. 15) supported by a trestle. A series of grooves under the
beam permits it to be placed at any angle. The beam (different from
that used by curriers) may be of wood, iron, steel, or zinc-covered
wood.

  [Illustration: FIG. 17

  DEHAIRING KNIFE]

There are several types of unhairing machines, of which the Leidgen
more nearly approaches hand work than any other. The skins are placed
on a soft bed of felt, and the working roller, fitted with spiral
knives, is brought into contact with the hide and scrapes off the
hair.

  [Illustration: FIG. 18

  DEHAIRING AND FLESHING MACHINE]

The type of machine often used, however, is shown in Figure 18;
the working part is a long spindle fitted with helical knives. The
advantages of this machine are its large output and its use for other
operations by simply changing the working roller. The blades must be
blunt for dehairing, but sharpened blades are needed for fleshing.

If hides intended for sole leather are being dehaired, the short
hairs which are not removed by the dehairing knife are carefully
scraped off with a sharp knife. Other kinds of hides and skins are
freed from short hairs in a later operation.

When the hides are dehaired, they are sometimes submitted at once to
the next operation of fleshing, which, as its name implies, consists
in removing loose flesh and fat from the "flesh" side, that is, the
side near the carcase. The extent to which this operation is carried
out depends on the quality of the finished leather. Naturally, the
more flesh left on the greater the weight, particularly as loose
flesh will absorb a large quantity of tannin, and, unfortunately, of
adulterants which are frequently used for weighting common leathers.
The flesh ought to be removed in all cases, for the loose flesh forms
very poor and spongy leather. Where hides and skins are tanned and
then dried for sale to leather dressers and finishers, there is often
the tendency to leave far too much loose flesh on them, with the
object of producing as much weight of leather as possible. From the
point of view of economy, this is a mistake, for the loose flesh must
be removed during the dressing process, whereas, if it had been taken
off at first, both material and time would have been saved in the
process of tanning.

If the fleshing is not done directly after dehairing, the hides or
skins should be placed in a weak lime liquor, and this method is
to be recommended. The great point to be observed is to keep the
limed hides, both before and after dehairing, away from contact
with the air, as the chemical action of the carbonic acid on lime
results in the formation of chalk, which tends to harden the hides
and to roughen the grain, so that it is likely to be scratched in
later operations. Where the hides are intended for sole leather, and
not treated with an acid before entering the tanning liquors, the
presence of chalk would lead to an uneven colouring of the leather.

  [Illustration: FIG. 19

  FLESHING KNIFE]

Fleshing by hand demands great skill. The knife used (Fig. 19) is
similar to the unhairing knife, except that it has two edges. The
cutting is done with the convex edge, which has to be kept very
sharp. The concave edge need not be sharp, its use being limited to
scraping off loose particles of flesh, while the parts not removed
by this means are cut off with the sharp edge. The knife is held
slantingly, with the blade almost parallel with the beam. The
strokes should be short and in a semicircular direction, otherwise
it is difficult to avoid cutting the skins. This manual operation
is now largely superseded by machinery, and will, no doubt, soon be
obsolete. The early types of fleshing machines were not a success,
but the modern machine is very effective. There are several makes
on the market, but in most cases the working tool is of similar
construction and consists of a long cylinder to which spiral knives
are fixed. (Fig. 18.) Half of these blades converge to the left and
half to the right, the object being not only to cut away the flesh
but also to stretch the hides outward, thus ensuring an evenly cut
surface. The fleshings and useless pieces of skin are kept in a weak
lime liquor until there is a sufficient quantity to send to the
glue maker; although in some of the larger tanneries this offal,
technically termed "spetches," or glue pieces, is converted into glue
on the premises. In hot weather, a large accumulation of fleshings
is liable to putrefaction, despite the use of plenty of lime water.
While lime certainly arrests putrefaction of gelatinous matter for
a time, decomposition afterwards sets in and serious damage may be
done. To avoid this, it has been a common practice in Germany to use
formaldehyde, but, while this acts as a preservative, it hardens
animal tissues, and has a tanning effect, with the result that the
pieces are rendered insoluble and cannot, of course, be reduced to
a liquid gelatine by boiling. Glue makers have condemned the use of
formaldehyde, but other preservatives, such as "lysol" (a cresylic
compound) and "arasol," have no tanning effect and may be used with
safety.

After the operation of fleshing, it is necessary to get rid of the
lime in the hides, for, if they were put directly into tan liquors,
the lime, being alkaline, would neutralise the acidity of the tan
liquors and retard the beginning of the tanning process for a long
period. The leather would ultimately be poor, thin, stained, and
brittle.

Up to the process of deliming, there is not a great deal of
difference in preparing the hides and skins for the large variety
of leathers, but between the fleshing and the tanning processes
the work varies considerably, and largely determines the character
of the finished leather. When the hides or skins are in the limed
state, they are gristly and firm in texture. A certain amount of this
firmness is desirable in some leathers, such as sole and belting,
and, therefore, it is deemed advisable to leave a small quantity of
lime in the hides, although, to get them evenly coloured in tanning,
it is essential that the lime should be completely removed from the
surface of the hide. An old method, which is even in use to-day
in some tanneries, is to wash the fleshed hides in a cubical or
hexagonal drum for several hours in running water, which is conveyed
through an iron pipe in the journal of the drum, and escapes through
small holes in the drum. The effect of using a hard water for washing
out the lime is shown in the interior of these washing drums, the
sides of which become incrustrated with a thick, hard deposit. The
surface of this incrustration is irregular, and small projections are
sometimes formed which mark the hides and reduce their value, as the
impressions are not removed in later processes.

The modern method of deliming hides intended for sole leather is
to use a weak solution of acid, or an acid salt. For this purpose,
sulphuric and hydrochloric acids are by far the cheapest, but require
handling with great care, as any excess used has a corrosive and
destructive effect on the fibres, which results in weak leather.
Mild organic acids are much safer, and those generally preferred
are lactic, formic, and butyric, although boracic and acetic acids
are favoured by some tanners. Butyrate of ammonia is used for the
same purpose by a number of French tanners. The same acid bath can
be used for a second lot of hides, but sufficient acid should be
added to raise the acidity of the liquor to its former standard. It
is inadvisable to use one bath more than four or five times. The
salt formed during the process by the combination of the lime with
the acid--calcium lactate, formate, butyrate, acetate, or borate,
according to the acid used--must be washed from the hides, either in
a pit or drum, before they are ready for the tan liquors.

  [Illustration: FIG. 20

  SCUDDING KNIFE]

Other kinds of hides and skins require additional treatment,
according to the class of leather it is intended to make. Hides to
be dressed for such purposes as bags, portmanteaus, cases, harness,
belting, and stout uppers are usually steeped in an infusion of hen
or pigeon dung. A vat is filled with tepid water, a quantity of the
dung, usually about half a pailful, is added and well stirred in the
water before putting the hides in. The acid fermentation evolved
neutralises the lime, while bacteria multiply and rapidly reduce
the rubbery limed hide to a soft, flaccid condition. The hides are
then well washed in clear water and scudded, after which they are
transferred to the tan pits. "Scudding" is the technical name of an
operation performed on hides and skins with a special tool, known
as the scudding knife, which consists of a convex piece of slate or
vulcanite fitted into a wooden or steel handle (Fig. 20). The hides
are placed on the beam, grain side up, and vigorously worked with
the knife to scrape off scud (_i.e._, short hairs, dirt, and soluble
lime salts). Both sides of the hides should be scudded for best work.
The process of treating hides with excrement is known technically as
"bating,"

Calf skins, which are curried or dressed after tanning, should be
reduced to a more supple condition than hides intended for harness,
belting, and military leathers. A more active dung is, therefore,
used for skins of all kinds which have to be rendered supple. Dog
manure is generally used, that from the hunting kennels being
preferred. Imported dry dung has to be used by some firms, as the
supply of fresh dung is insufficient. The demand for the latter is
very keen, as it is more effective than the dry product. Goat skins
dressed for the famous shoe leather known as glazed or _glacé_ kid,
and kid skins for glove leather, need a larger proportion of "puer"
than nearly every other kind of leather, for the grain of goat skins
is naturally hard and requires a large quantity of dung to reduce it
to the necessary softness and suppleness of "kid" leather.

Although these processes can only be described as disagreeable, they
apparently have no injurious effect on the workmen. Further, the
hides and skins are thoroughly cleaned before putting them in the tan
liquors, in which the bacterial activity caused by the infusion of
dung is quickly arrested.

Fortunately, from the hygienic point of view, the use of natural
"bates" and "puers," although still extensive, is likely to be
superseded everywhere by artificial products. So far there are nearly
2,000 tanneries throughout the world where the artificial bating
materials are preferred, German and American tanners being the
principal users.

The best known artificial bate is "Oropon," which consists of a
mixture of pancreatin or trypsin, ammonium salts, and a large
quantity of sawdust, the last-named merely acting as a mechanical
agent. The enzyme, pancreatin, is the active ingredient, and may
be prepared from the intestines of the pig. It has the effect of
breaking up the albuminous matters of hides and skins, which are
rapidly reduced to a soft and supple condition, while the ammonium
salts cleanse them. The quantities used vary according to the degree
of suppleness required in the finished leather.

The patentee and vendor of this proprietary article claims that
it is suitable for all classes of leather. Hides for sole leather
are sometimes treated with a weak "Oropon" liquor in Continental
tanneries and, as a result of the cleansing properties of this
bating material and its effect in opening up the fibres, the tannage
proceeds rapidly. The use of enzymes for bating was discovered by
an English leather manufacturer and chemist, who did not take out a
patent for his invention, probably because he had previously patented
and worked on a commercial scale a bacterial bate which gives very
good results but requires much skill in application.

The artificial product, "Oropon," has many advantages over
excrements. It is simpler, cleaner, and more rapid in working, and
never damages the grain of the skin. On the contrary, great care
and experience are needed in using excrements, and the skins may be
so badly damaged through negligence as to be almost worthless. Bate
burns are fairly frequent when dung is used, and are generally due to
hard pieces being insufficiently broken up and diffused in the liquor.

Other useful artificial products are: "Erodin," and "Puerine," a
patented American product which consists of a weak organic acid and
a small proportion of molasses. Possibly, malt enzymes or diastase
could be utilised for the manufacture of an artificial bate or puer,
although they would not be so effective as animal products.

Where hides and skins have been treated with Oropon, they may be
transferred to the tan liquors after being rinsed in water, although
it is better to submit them to the operation of scudding.

There are two tests to determine the end of the process of bating
and puering, although the extent to which the reduction is carried
depends on the kind of leather wanted. For this reason, it is not
advisable to remove every trace of lime from hides which must possess
a certain degree of firmness when finished into leather. Of the two
tests, one is chemical and the other mechanical. In the former case,
a cross section is made in the thickest part of the hide and a few
drops of phenolphthalein are added to the cross section; if the whole
of the lime has been removed, no coloration is given, but, if lime
be present, a purplish colour is given, which varies in intensity
according to the contents of lime in the hide. The other test is made
by pressure with the thumb nail, and, if the impression be permanent,
the hides or skins are in a sufficiently reduced, or, as it is
technically known, "fallen" condition for all practical purposes.
The latter test is really only useful when the process has to be
carried to its fullest practical extent, as it affords no idea of the
intermediate stage. The experienced workman can judge the progress
made by appearance and touch.

In cases where skins have been puered with excrement it is often
necessary, after scudding them, to submit them to a further process
before tanning. This is known as "drenching," and consists in
treating the skins in an infusion of wheaten bran or pea flour. The
acid fermentation produced by these ingredients effectually cleanses
the skins by neutralising the last traces of lime and scud, and
prepares them in an ideal condition for the process of tanning. The
combined processes of bating with Oropon and drenching in bran are
extremely useful for skins to be dressed into glove leather.

Following the processes of bating, puering, or drenching, the skins
are washed in water to remove all mechanical impurities, and are then
in a perfectly clean condition for tanning.



CHAPTER VI

TANNING PROCESSES


The methods of tanning may be classified as follow: (1) Vegetable
tanning processes; (2) methods of chroming; (3) tawing processes; (4)
oil tannages; (5) formaldehyde tannages; (6) sundry tannages, chiefly
mineral; and (7) combination tannages. The public is chiefly familiar
with types of vegetable tannage in boot sole, bag, and portmanteau
leathers; of chrome tannage, in box calf and glazed kid used for boot
uppers; of the tawing process, in kid glove leather; and of the oil
tannage in wash leather or "chamois."


VEGETABLE TANNING PROCESSES

The methods of tanning with infusions of barks, leaves, and fruits
of trees and plants containing tannin are much more numerous than
they were a decade ago, and tanners have now to pay special attention
to the selection and blending of the materials they use in order to
produce the various qualities of leather required. Formerly, most of
the sole leather was tanned in oak bark liquors, and, in the later
stages of the process, valonia and gambier were added to quicken the
process and give solidity to the leather. This tannage, which may be
described as an oak bark tannage, is still used by a few tanners,
but the wide choice of materials available has brought other tanning
agents into prominence, chiefly because they possess more astringent
properties, and, therefore, tan more quickly than oak bark. Moreover,
the need of other materials than oak bark became a necessity several
years ago, as the supply of the latter would be inadequate to
produce the large quantity of leather now required, even allowing
for the rapid development of mineral tannages. Further, it is amply
proved that a good blend of materials (mixed tannage) produces quite
as durable and a firmer leather than the old oak bark tannage;
unfortunately, there are other blends, occasionally combined with
extraneous weighting materials, which account for the poor quality of
a great deal of modern sole leather.

While the mixed tannage is now popular for sole, belting, harness,
and other heavy leathers, vegetable tanned light skins, such as calf,
goat, and sheep, are in most cases treated with a single material,
sumach being used for a good proportion of them.

Whichever method be used, the first essential is the most suitable
means of leaching the materials, or extracting the tannin. It seems,
however, that this process may be eventually eliminated from the
tannery, for most tanning materials are now converted into extracts,
which only require dissolving in water to prepare the tan liquor. The
manufacture of tanning extracts is quite a separate business, which
is generally, but not always, conducted in factories situated near
the source of the raw materials. There are important extract works in
the Argentine, Paraguay, Canada, the United States, Hungary, North
Germany, Borneo, Smyrna, France, Italy, and England.

  [Illustration: FIG. 21

  BARK MILL]

Where natural tanning materials are used, either entirely or in
conjunction with extracts, the leaching is done in a series of large
square pits, four of which would suffice for a small yard, while a
very large tanning would need twelve or sixteen. Oak bark, which is
usually delivered to the tannery in strips measuring 3 to 6 ft. in
length, must be chopped or ground into small pieces by machine (Fig.
21). A measured quantity (a certain number of baskets or skeps full)
is placed in the empty pits, which are then filled with water. The
liquor is pumped from these pits, as required, to others in which
the hides are tanned. The hard fruit of myrobalans, which somewhat
resembles nutmegs, is powdered in a disintegrator or special crusher.

  [Illustration: FIG. 22

  TAN-YARD

  ("Dri-ped" Tannery)]

  [Illustration: FIG. 23

  HIDE ROUNDED FOR SOLE LEATHER]

The three principal vegetable tannages are those for sole, dressing,
and light leathers, and it is obvious that a careful selection of
materials is necessary to obtain the desired effects. For this
reason, oak bark, although a good tanning material for dressing
leather, is insufficient to produce a firm sole leather, and,
therefore, even in the so-called pure bark tannages, valonia or other
suitable tannin is used towards the end of the process in order
to increase the solidity and waterproof quality of the leather.
There are two general methods of tanning sole leather, namely,
the pit and the drum tannage. In the first case, the hides are
passed through three series of pits containing gradually increased
strengths of tannin (Fig. 22). These series are technically described
as "suspenders" or "colouring pits," "handlers," and "layers" or
"layaways." To facilitate handling and economise tanning materials,
hides are "rounded" (_i.e._, cut into sections) either before tanning
or after the hides have passed through the suspenders (Fig. 23). The
obvious advantage of the former method is that the offal (shoulders
and bellies) removed can be chrome tanned if required. The suspenders
may consist of any number of pits from six to twenty-four, according
to the size of the tannery. As the name implies, the hides are
suspended in the liquors from poles, which extend across the top
of the pit. The hides are attached to the poles by means of stout
cord or copper hooks. Various mechanical appliances are in use to
supersede the old method of allowing the hides to rest during this
process. These methods save time and tend to produce even coloration,
the latter being a very important point in the early stages of
tanning. Some of the methods advocated, however, are too vigorous for
the hides at this stage, when the chief object should be to preserve
as much gelatine as possible. The best mechanical system is that
which gently raises and lowers the hides in the liquors. Some of the
American tanners use a mechanical contrivance known as the rocker,
which consists of a stout wooden beam rocking from a central pivot,
and with a see-saw movement. The objection to this method is that the
hides do not receive equal treatment, those in the centre receiving
hardly any movement, while others at the ends of the beam are raised
too far out of the liquor. Under these conditions, the colouring of
the leather must be irregular. Another method, invented in England,
consists in suspending the hides from a wooden frame which can be
mechanically moved on wheels.

As the contact of tanning liquors with iron must be avoided to
prevent discoloration (iron and tannin form the basis of inks),
the wheels should be galvanized. This mechanical method is very
satisfactory, for the hides are moved gently and kept in the liquors.
As some tannins oxidise rapidly (_i.e._, darken in colour by exposure
to the air), any process which exposes the hides at this stage for
lengthy periods should be avoided.

  [Illustration: FIG. 24

  BARKOMETER]

The theory of the vegetable tanning process is not perfectly
understood, and the principal trade chemists are not yet agreed as
to whether the changes are chemical, physical, or both. Many are
inclined to believe that both changes take place, and this view
is probably correct, as a pure tannic acid produces a thin, empty
leather, while a tanning material which contains a fair proportion
of non-tannin matters, yields a full and firm leather. The practical
tanner who adapts his work to the theory that tanning is a process
of feeding the hides with gradually increasing strengths of tannin,
is, in any event, on the right track. The suspender liquors are
always weak in tannin, and are pumped from "handler" liquors
through which packs of hides have already passed. It is important
that these liquors possess a certain degree of acidity, and, if
the natural acids of the tan liquor are too weak, or neutralised
completely by the lime in a pack of hides that has been treated, a
small quantity of acetic, formic, or lactic acid is added. Formic
acid has the additional advantage of making the liquor antiseptic.
It is absolutely necessary that the liquors have acid properties,
otherwise tanning cannot proceed. Acid assists penetration of tannin.
Hyposulphite of soda, formaldehyde, or synthetic tannin may be used
for the same purpose, while these also help to keep the leather
light in colour, owing to their bleaching properties. After passing
through three or four suspender pits, in which the tan liquor is
gradually strengthened, the hides are often rounded and the butts
(Fig. 23) are transferred to the handlers. The first handler liquor
should register about 25 degrees by the barkometer (Fig. 24), an
instrument which registers the density of tan liquors. The handlers
consist of a series of six or eight, and the strength of the liquors
should be increased gradually. After a day's immersion in the first
handler liquor, the hides are hauled out with a sharp two-pronged
hook fixed to the end of a long wooden pole, similar to that used in
the liming process. After they have been piled up for a few hours,
two workmen, one on each side of the pit, place the hides flat in the
next pit. The tan liquor is then run off the first handler to the
suspender and fresh liquor is pumped into the empty pit, which then
becomes the head or strongest liquor of the series. The succeeding
packs will, therefore, follow in rotation: the first going to No.
2 pit, the second to No. 3, and so on. In the last two or three
handler pits, the hides are sometimes dusted with freshly ground
tanning material, such as oak bark, myrobalans, or divi-divi, the
object being to strengthen the tan liquor so that it penetrates the
hides before they are transferred to the layers. The handler liquors,
which are originally sent back from the layers, are also frequently
strengthened by the addition of oakwood, chestnut, or quebracho
extracts, although some tanners only use extracts in the layers.
Gambier is a useful material at this stage, as it keeps the liquors
mellow and plumps the leather. In the layers, the last series of tan
pits, the hides are treated with very strong extracts, and are also
heavily dusted with such natural tanning materials as give firmness
and solidity to the leather. For this purpose, nothing is better
than valonia, or valonia extract, which deposits a large quantity of
bloom, or ellagic acid. Where a mixed tannage of natural materials
is used, the density of the liquors may reach 50 degrees barkometer,
but if strong extracts be added, the barkometer may exceed 100
degrees. The relation between the layers and handlers in regard to
the disposal of the used liquors is similar to that between handlers
and suspenders; the first layer used is sent to the last handler.

By the English method, the leather is not, as a rule, transferred
immediately from one pit to another, as it is found preferable to lay
the hides in pile for a few hours, by which means the great weight
helps to force the tannin through them. By draining the hides, they
are in good condition for the absorption of the next tan liquor.
The English method of handling is too slow for most of the American
tanneries, where the greater proportion of the hides are cut straight
down the centre to form "sides," as they are technically known. In
America, the pieces of leather, whether hides, butts, bellies, or
shoulders, are often tied together and transferred from one pit
to another by means of a skeleton reel, worked either by hand or
mechanically. The latest type of reel is a great improvement on the
old reel. The cost of manual labour in many English tanneries is
very great, in view of the fact that the hides have to pass through
many pits, and the work of transferring the hides from one pit to
another is done entirely by hand. It seems that there is plenty of
scope for mechanical ingenuity in overcoming this difficulty, and it
may yet be found possible to construct a perforated brass platform,
connected with a crane, by which the whole of the hides could be
lifted out in a second, left to drain for half an hour or more, and
then bodily transferred to, and lowered in, the next pit. Naturally,
it is easier, and quite within the bounds of practicability, to raise
the hides from suspenders by mechanical power, as it would not be
difficult to fix a stout cross-beam to the pulley from which the
hides are suspended. The leather can be safely treated with very
astringent tannin in the last series of pits, and the use of strong
extracts is, therefore, a common practice at that stage, not only to
give solidity and firmness to the leather, but to increase its weight.

It would be quite fatal to the production of good leather if strong
tannins were used in the early stages of the process, because the
surface on both sides would tan quickly, the grain of the hide would
be badly drawn owing to the sensitiveness of gelatine to astringent
solutions, and it would be impossible to make the tannin penetrate
the hide. The final product would be a half-tanned leather which
would be extremely brittle and poor in quality; in fact, quite
unsuitable for sole leather. Despite the well-known axiom that the
vegetable tannage (but not the mineral) must proceed slowly and
gradually in the early stages of the process if the hides are to be
properly tanned, the modern tendency is to speed up the tanning, with
the result that, in some cases, the so-called sole leather is really
not fit for the purpose for which it is intended. The root of the
evil is the desperate attempt made by many boot manufacturers to
produce lower-priced boots than those of their competitors.

Taking into account the development of leather trades chemistry, it
is not surprising that the problem of reducing the time required to
complete the old processes of tanning has received much attention.
The results have been successful in some instances and have certainly
proved that very good sole leather can be made without leaving the
hides in the pits for a year or longer.

It has also been shown that the absorption of tannin can be
accelerated by treating the hides, before putting them in the
suspenders, with a solution of acid (lactic or butyric for
preference), or hyposulphite of soda, or synthetic tannin. The latter
penetrates the hides in a few hours without contracting the grain,
increases the solubility of the vegetable tannins subsequently
used, and helps to keep the leather light and uniform in colour.
It is of no use alone for heavy leathers, however, as it lacks the
physical properties necessary to make the leather firm and resistant
to water. The use of "soluble" oils in the tan liquors is another
late innovation which has given good results. The term "soluble" in
connection with oils merely means that they are made miscible with
water by treating them with acids. Solubilised cod oil might be
specially useful, as it has tanning properties and would increase the
wearing and waterproof qualities of the leather. The chief objects
of using oil in tanning, however, are to increase the weight of the
leather and permit the use of strong liquors.

The tanning process outlined is the oak bark tannage, which is now
supplanted in many yards by the mixed tannage, in which various
tannins, chiefly exotic, are skilfully blended to produce the kind of
leather wanted. Each tannin seems to have special characteristics,
although the materials are classified into only three groups, namely:
pyrogallol, catechol, and mixed (pyrogallol and catechol) tannins.
Generally, the best mixed tannages for solid leather consist of a
combination of both pyrogallol and catechol tannins. Reviewing the
characteristics of some of the principal tanning materials, it may
be said that oak bark produces a nice, fawn-coloured leather of
strong texture, but tans slowly; valonia makes the leather solid,
durable, and waterproof; myrobalans quicken the process and lighten
the objectionable colour of other tannins; divi-divi and algarobilla
are very rich in tannin, and are, therefore, useful in later stages
of the process; gambier mellows the astringency of other liquors
and plumps the leather; while most of the tanning extracts on the
market penetrate the hides much more quickly, often give a lighter
colour than that produced by solutions of the natural materials, and
expedite the process considerably.

The most popular tanning materials are: oakwood, quebracho, chestnut,
valonia, myrobalan, mangrove, mimosa, hemlock and spruce extracts,
oak bark, valonia, gambier and sumach. The following are some of the
combinations in use--


_For Sole Leather._

1. Oak bark and valonia, or valonia extract.

2. Oak bark, valonia, and gambier.

3. Oak bark, quebracho extract, and myrobalan extract.

4. Chestnut, quebracho and valonia extracts.

5. Chestnut and oakwood extracts.

6. Oakwood and quebracho extracts, and divi-divi or algarobilla.

7. Quebracho extract, myrobalans, and valonia.

8. Quebracho, mangrove, and valonia extracts.

9. Oakwood, mimosa, and valonia extracts.

10. Hemlock and oak extracts (American union tannage).


_For Dressing Leathers._

1. Oak bark and sumach.

2. Oakwood and quebracho extracts, and sumach.

3. Synthetic tannin and oakwood extract.

4. Synthetic tannin and myrobalans.

5. Gambier and sumach.

6. Wattle bark and myrobalans.

Sumach is often used alone for some classes of goat, sheep, and calf
skins. Synthetic tannins can also be used alone for light leathers.

Many other variations may be tabulated, for nearly every tanner has
his own recipe, having found by experience the blend of tannage that
best suits his trade.

Apart from these innumerable combinations, the only method whereby
the vegetable tanning process may be hastened is the mechanical, for
which purpose either the paddle (Fig. 25) or the drum (Fig. 13) is
used. The former consists of a wheel constructed of wooden shelves
which, when in motion, dip a little way into the tan liquor in a
vat, and so keep it in constant circulation. The drum is fitted
inside with wooden shelves or pegs, which carry some of the hides
or skins to the top of the drum at each revolution. Were it not for
these shelves, the tannage would probably be irregular or otherwise
unsatisfactory, as the hides would always be heaped together at the
bottom of the drum. The paddles and drum are more often used for
light than for heavy leather, as they not only have the effect of
making the leather loose on the grain, but also make it soft and
supple, characteristics which are not required in most of the heavy
leathers.

  [Illustration: FIG. 25

  PADDLE VAT]

However, the drum is now largely used on the Continent for the
tannage of sole leather. A great saving in the cost of production
is thereby effected, but the leather, although of satisfactory
appearance, lacks the durability and waterproof quality of pit-tanned
leather. The process is much simpler than the pit method, and less
room is required. There are only two stages of tanning: (1) by
placing the hides in colouring pits or suspenders, in which the
hides are nearly struck through with tannin; and (2) running them
in slowly-revolving drums containing solutions of tannin which are
gradually strengthened until the process is finished. There can be
no doubt that the tannin is rapidly forced between the fibres of
the hide by mechanical action, but it is not so firmly combined as
that slowly absorbed by the hide in the pit method. This can be
proved by placing two pieces of weighed leather--one tanned in pits
and the other in a drum--for twenty-four hours, drying the leather
and reweighing it, when it will be found that the drum-tanned
leather has lost the greater percentage of weight. To obviate this
disadvantage as far as possible, use is made of special oils, which
serve to fix the tannin more firmly between the fibres and render the
leather more resistant to water. Other frequent drawbacks of drum
tanning are looseness of grain and lack of substance. In sole leather
tanning, the former is modified to some extent by extra pressure in
rolling the leather during the finishing operations; while the latter
difficulty is sometimes overcome by swelling the leather with acid
and then fixing the swollen condition of the hide by treating it
with a weak solution of formaldehyde. This chemical also has tanning
properties, so that the process is hastened; but leather prepared in
this way cannot be as durable as that produced by a natural tannage.

It seems that the aid of the engineer is necessary to overcome the
difficulty of looseness of the grain caused by the severe pounding of
the hides in the drums. The constant circulation of the tan liquor is
required, but the hides should only be subjected to gentle motion.
It is true there are tanning drums on the market which are said to
obviate all the difficulty found in making sole leather in ordinary
drums fitted with shelves or pegs, but a drum that meets the ideal
conditions for the production of a solid yet flexible sole leather
has not yet been invented. It seems that a kind of inner framework,
to which the hides can be attached and which rotates much more slowly
than the main drum, may solve the problem. The drum tannage permits
the use of an excessive quantity of tannin, which, of course, adds to
the weight of the leather. By the drum method of tanning, heavy hides
can be tanned in two days after leaving the colouring pits; lighter
hides are, naturally, tanned in less time, proportionate to their
substance. The pit method occupies any time from one to fifteen
months, although nowadays very few hides are left in the tan pits for
a year.

The methods of tanning just described relate chiefly to sole
leather, but there is an enormous production of leather known as
dressing hides, which are tanned, dried in the rough state, and
sent to curriers or leather dressers for finishing. These hides are
used for numerous purposes, including bags, portmanteaus, harness,
saddlery, straps, belting, and boot uppers. The tannage of dressing
hides differs slightly from that of sole leather; the liquors must
be mellower and contain less insoluble matter, in order to obtain
the necessary pliability, and a good, clear colour on the grain.
A satisfactory tannage is obtained by treating the hides in oak
bark liquors, which, in the later stages of the process, may be
strengthened with oak wood, or myrobalan extract, or pure gambier,
and completing the process in a tepid bath of sumach, which clears
and lightens the colour. The drum is more suitable for the tannage of
dressing hides than it is for sole leather. A quick method of drum
tanning would be to treat the hides first in a 5 per cent. solution
of neradol, the artificial tannin, and then complete the process
with oakwood, chestnut, or quebracho extracts, or even in mixtures
of these extracts. In this way, fairly good leather could be made in
about two days. Neradol prevents the drawn grain and dark coloration
that would result from the use of vegetable extracts alone.

In the case of light skins, such as calf, goat, and sheep, the
method of vegetable tannage again differs from those just described,
although there is a fair quantity of calf skins tanned with oak bark,
especially those used in the shoe trade. The tendency, however, is
to complete the process rapidly by using extracts, such as oakwood,
quebracho, or mimosa. A very good tannage for the production of a
mellow and plump leather is that of pure gambier, the colour produced
forming a good ground for brown shades. Where light, fancy colours
are required on the finished leather, this tannage must be completed
by placing the skins in a tepid bath of sumach.

A large proportion of the vegetable-tanned sheep and goat skins
is produced by sumach alone, which was adjudged by the Commission
appointed a few years ago by the Royal Society of Arts to investigate
the cause of decay in bookbinding leather to be the best tanning
material and the one least affected by exterior conditions, such as
gas, sunlight, air and dust.

Many sheep skins are split into two sections by machine before
tanning, the top portion, known as the grain, being tanned in sumach,
and described as "skivers." The under section, the side near the
carcase, is known in the trade as a "lining," and is usually made
into the so-called "chamois" leather by means of the oxidation of
fish oils.

Other noteworthy vegetable tannages are those used in the production
of Russia leather, and a large proportion of East India leather.
Real Russia leather, of which the raw material consists of small
native hides and calf skins, has a characteristic and pleasant odour,
which is derived from the birch and willow barks used in the tanning
process. Birch bark contains an essential oil, which is permanently
fixed on the fibres of the leather during the process of tanning.
This leather is only produced in Russia, and chiefly in one large
tannery, although imitations are made in Great Britain, America, and
Germany. These are produced by the use of ordinary tanning materials,
and the scent is applied, either during or after the dyeing process
by the addition of birch tar oil, which is made by the distillation
of birch bark. In some respects, for example, in brilliance of
finish, smoothness of grain, and freedom from defects, the imitation
is better than the real, but the latter has the great advantage
that its perfume is of superior fragrance and permanent, whereas
the imitation leather only retains the odour for about a year. It
is somewhat remarkable, in view of the good demand that exists for
the leather, especially in England and Germany, that no firm outside
Russia has thought it worth while to produce the genuine article. The
tannage would be particularly serviceable for bookbinding leather, as
the oil of the birch has both insecticidal and antiseptic properties.

The principal vegetable tannage used for Indian leather, namely,
the bark of the _acacia arabica_, known to the natives as babul,
or babool, has quite a contrary effect, for it contains a large
quantity of red colouring matter, which is incorporated with the
leather in the tanning process, and although it shows very little
in the rough-tanned leather, it is apt to darken if the finished
leather is exposed to strong light for a long period. This oxidation
is accompanied by a gradual weakening of the fibres of the leather,
which is, therefore, quite unsuitable for bookbinding. Fortunately,
Indian tanners are making rapid progress in using other tanning
materials, a good number of which are found in India.

Although the bark of the _acacia arabica_ is not altogether
satisfactory, the pods of the same tree, which are commercially known
as "bablah" and contain nearly twice as much tannin as the bark,
produce a very light-coloured, almost white, leather, and it is
asserted that this material is a valuable substitute for sumach.


MINERAL TANNAGES

By far the most important of the mineral tannages is the chrome
process, the merits and demerits of which have not only been
freely discussed in the trade, but also in the lay press. Fanciful
theories of the poisonous character of this kind of leather have
been published from time to time in the daily press. Such absurd
statements as that prussic acid and mercury are used in the
manufacture of chrome leather hardly need refuting, as, even if they
could convert skins into leather, the cost would prohibit their use.
The only poisonous acid used in one of the many chrome processes is
chromic acid, but this is converted into the oxide of chromium in a
second bath and is, therefore, made quite innocuous.

The chrome tannage is effected either by the one-bath method or the
two-bath. In the former case, the tanning agent, either a basic
chromium sulphate or chloride, is present in the one liquor used; in
the latter method, the hides or skins are impregnated with a solution
of chromic acid, which is reduced to chromic oxide in a second bath
consisting of sulphurous acid and a small quantity of free sulphur.
The properties of leather produced by the two-bath process render it
especially suitable for vulcanising on rubber; hence its large use
for non-skidding bands for motor tyres.

There are several recipes for making one-bath liquors. A favourite
mixture consists of chrome alum and sodium carbonate (common soda).
Another method consists of reducing a solution of chromic acid with
glucose or grape-sugar. This liquor has a greater plumping effect
on the leather than the chrome alum liquor has. A third process of
making a one-bath liquor combines the use of bichromate of potash and
chrome alum, which, when dissolved, is converted into a basic chrome
salt by means of a reducing agent. The one-bath liquor can be easily
and safely applied to hides and skins, and is used in much the same
manner as a vegetable tan liquor, beginning with a weak solution and
gradually increasing the strength until the process is completed.
The two-bath method needs great care, as a slight difference in the
proportions of the ingredients used may alter the character of the
leather produced.

The formula now largely used is practically the same as that of the
original patentee, Augustus Schultz, an American chemist. The first
bath, the chromic acid solution, is made by treating bichromate
of potash or soda with hydrochloric, sulphuric, or formic acids.
Bichromate of potash and hydrochloric acid (commonly known as
muriatic acid, or spirits of salts) are commonly used, and in the
proportion of 5 per cent. and 2-1/2 per cent. of the weight of the
drained pelts (5 lb. of bichromate and 2-1/2 lb. of acid for 100 lb.
of pelts). The chemical reaction is represented by the following
equation--

    K_{2}Cr_{2}O_{7} + 2HCl = 2KCl + 2CrO_{3} + H_{2}O

    Bichromate of potash + Hydrochloric Acid
    = Potassium chloride + chromic acid + water.

This process is most conveniently carried out in the paddle-vat
(Fig. 25), which, in this case, should be fitted with a wooden cover
to exclude light, since the colour of the chromic acid liquor is
affected by strong light. Some chrome tanners prefer to use the drum
tumbler (Fig. 13), but the pounding of the skins by this method is
apt to make the grain loose. Whichever method be adopted, the hides
or skins should be horsed up to drain for several hours before
transferring them to the second bath. It is important that they be
placed grain to grain and smoothed out, as creases and air bubbles
between the skins become fixed in the second liquor, and depreciate
the value of the finished leather. To avoid this danger, many tanners
pass the hides or skins through a striking-out machine under light
pressure. Another detail of importance is to cover the chromed skins
with canvas or matting to keep them from the light. Although the
skins are preserved by chromic acid, they are not made into leather,
for in this condition they would dry quite horny. Hence, it is
undesirable that the hides should be dried at this stage and sold
as leather, although such a proceeding has been attempted. Further,
chromic acid is an irritant poison which may cause an eruption on
the hands and arms of workers handling the hides in this solution,
unless they are protected by rubber gloves, or by coating the hands
with a mixture of vaseline and lanoline. The second bath consists of
chemicals which reduce the chromic acid to the oxide, which is quite
inert, so that there is no danger whatever of contracting a poisoned
foot as the result of wearing chrome leather. The chemicals largely
used for the second bath are hyposulphite of soda and hydrochloric
acid. Sodium sulphite may also be used without the addition of acid.
The skins change from an orange colour to a pale, bluish-grey tint,
but the process is not completed until a cross section shows that
the colour has changed right through the skin. A suitable proportion
is 10 per cent. "hypo" and 2-1/2 per cent. acid (28° Twaddell)
calculated on the weight of the drained pelts. Calf, goat, and sheep
skins are usually treated in the drum, but hides, especially if a
certain degree of firmness is required, are preferably run in the
paddle-vat. The reaction of the chemicals in the second bath are
somewhat complicated, but the principal point is the reduction of the
chromic acid (CrO_{3}) to chromic oxide (Cr_{2}O_{3}).

The sulphurous acid produced acts as the reducing agent, but is not
freely liberated until towards the end of the process, the skins
first changing into a dirty brown colour which gradually gives place
to a beautiful pale-bluish tint. The last stages of the process are
also marked by the formation of free sulphur, which aids materially
in softening the leather, and giving the two-bath chrome tanned
leather its characteristic rubbery texture. The vats in which this
process is carried out should always be fitted with lids to confine
the strong sulphurous fumes. By adding an excess of "hypo," the skins
can be bleached until they are nearly white. This has no harmful
effect on the leather, but makes it softer, though somewhat looser
on the grain. When completely tanned, the skins are horsed up again,
left to drain for at least twenty-four hours, and are then ready for
dressing and finishing.

The recipes for the one-bath process are numerous, but it is becoming
a common practice for tanners to buy the liquors or extracts already
prepared in chemical works, which are, naturally, better fitted
up for the production of a more uniform material than it would be
possible to make in most tanneries.


COMBINATION TANNAGES

Combination tannages have steadily grown in favour during the last
few years, and will probably have an important bearing on future
methods of tanning. Among those found practicable are: (1) Vegetable
and chrome; (2) vegetable and alum; (3) alum and chrome; (4)
synthetic and natural tannins; (5) synthetic and chrome; (6) alum and
synthetic; (7) formaldehyde and chrome; (8) chrome and iron.



CHAPTER VII

THE DRESSING, DYEING, AND FINISHING OF LEATHER


The dressing and finishing of leathers of all kinds seems to be of
growing importance every year, despite the fact that the durability
of leather is often impaired by the chemicals and heavy machinery
used in order to get a clear and bright colour or a highly-glazed
finish. One exception to this rule, however, is japanned and
enamelled leathers made by the new collodion-amyl acetate process,
which not only produces the so-called "patent" finish, but also adds
to the strength of the leather.

Dressing and finishing may be conveniently classified in four
sections--

1. Finishing of boot sole leather.

2. Dyeing and finishing of machine belting, strap, harness, and other
heavy greasy leathers.

3. Dyeing and finishing of boot, portmanteau, case, bookbinding, hat,
and upholstery leathers, and of the numerous fancy leathers.

4. Dressing, dyeing, and finishing of glove and chamois leathers.

There are also a few special kinds of leather which do not come
within the scope of this list. The limited size of this book makes it
impossible to outline the finishing of all kinds of leather, and only
a few of the important varieties can be referred to in the following
pages.


SOLE LEATHER

Formerly, the finishing of sole leather was a fairly easy matter, as
the slow process of tanning with oak bark which was in general use
gave the latter a nice fawn colour. The modern tendency, however,
is to demand even lighter-coloured leather than that produced by an
oak bark tannage, and, as most of the mixed tannages impart a darker
colour, the practice of bleaching has been universally adopted. This
process is to be greatly deprecated, since it reduces the strength
of the leather. Further, it has the serious drawback of removing
matters which would add to the waterproof quality of the leather, and
yet the boot manufacturers demand light-coloured sole leather. As in
many other articles of modern manufacture, quality is sacrificed for
appearance. The colour of sole leather is of no importance whatever
to the wearer of the boot, and the public should make a strong
protest against bleached sole leather, and also against leather
weighted with adulterants, if they wish to get boots of good wearing
quality. It is difficult to know where the finishing of some of the
modern sole leather begins. Formerly, the line of demarcation between
tanning and finishing was distinct, for the finishing processes were
begun as soon as the hides were sufficiently tanned. This is by no
means the case to-day, as, in many cases, the finishing may be said
to begin with a supplementary but unnecessary tannage in very strong
tanning extracts, with the object of making the leather firm and
plump, and, incidentally, imparting additional weight. This practice
would be discontinued if sole leather were sold by superficial
measurement. On the other hand, those who favour the continuance of
the present system of selling by weight assert that the adoption of
the measurement system would indubitably result in the production of
a lot of under-tanned leather, that mechanical means would be devised
to stretch the leather and thus give it an artificial area, and that
a fair quantity of the leather produced does not lie flat, and
would, therefore, be difficult to measure correctly. A great point in
favour of selling by measurement is that there would be no necessity
to weight the leather, and a mere visual examination would suffice
to determine the quality, whereas it is often difficult to state
whether leather has been treated with injurious artificial matters
or not, and certainly impossible to determine the extent of this
fraud, without a careful and somewhat elaborate analysis. Of course,
there are some rough practical tests for ascertaining the quality of
sole leather, especially in regard to the extent of its resistance
to water. A weighed quantity of the leather is soaked in water for
twenty-four hours, taken out, squeezed, dried, and reweighed. If
the loss of weight does not exceed 5 per cent., the leather is a
good sample and well tanned; on the other hand, it does not follow
that a loss, say, of 40 per cent., would indicate adulteration with
injurious materials, as the leather may have been tanned with an
excess of strong extracts which have not properly combined with the
fibres, with the result that the excess is easily removed in contact
with water. However, methods of fixing tanning extracts on the fibres
of the leather have been devised (see p. 117). A careful note should
be made of the time required to soak the leather through; if water is
absorbed rapidly, the leather is, naturally, unfit for soles.

After the tanner has taken great pains to produce the paleness of
tint required, the shoemaker buffs away the grain, thereby reducing
the resistance of the leather to wear, and then generally covers it
with a black, tan, or white dressing. In its turn, this finish is
likewise spoiled the first time the leather is worn. There could be
nothing more futile than the elaborate finishing of sole leather to
make it pale in colour, as it means that fully 80 per cent. of the
leather produced has to be bleached in some way or other; and the
manner in which this process is effected has a direct influence on
reducing the wearing quality of the leather. If, for example, the
colour of the leather is brightened with myrobalans, or sumach,
or with extracts of these materials, the wearing quality is not
affected; unfortunately, this method is not largely used, as it
does not increase the weight of the leather and would tend to make
it soft. A large proportion of sole leather is treated with strong
sulphited extracts, which both bleach and increase the weight of the
leather. In some cases, the leather is placed in vats containing
hot tanning extracts to increase the bleaching effect and add to
the weight. The gain of weight by this surplus tannage may be, and
often is, from 8 per cent. to 10 per cent., and, whereas the tanner a
century ago used to get only slightly above 50 per cent. of leather
on the weight of the raw hide, it is no uncommon thing nowadays to
get a yield of nearly 70 per cent.

The tanners are hardly to be blamed for this practice, which really
ought to be stopped; it is almost entirely due to the demand of
buyers for leather at a low price per lb., irrespective of its
superficial area compared with a higher-priced and often cheaper
article. It is only fair to state that those boot manufacturers who
have taken careful costings of their leather have not suffered great
loss in this way, but most repairers buy common leather in order
to be able to do their work at fixed prices usual in this trade. A
large proportion of this leather is under-tanned or weighted, and,
in either case, absorbs water like a sponge. This kind of leather
is quite unfit for soles, and ought to be condemned, as it not only
absorbs moisture but also retains it for a long time, so that it is
frequently a cause of colds and other complaints arising from chills.

If the repairer does not cost his leather as accurately as the
wholesale boot manufacturer, the latter often neglects to take into
account the quality of the leather, so long as cheap soles can be cut
from it.

The continual demand for leather which will yield low-priced
soles has brought about another practice which is much worse than
the use of hot extracts. In this case, the hides are not tanned
thoroughly, but, instead of completing the process with tanning
extracts, the leather is treated with cheap chemicals, such as epsom
salts (magnesium sulphate), glucose, and barium salts. These add
considerable weight and save the cost of expensive tanning materials;
further, it is claimed that they give increased firmness and
substance to the thinner parts of the leather, which otherwise could
not be used for soles. It is conceivable, therefore, that leather
of this kind could be cut to greater advantage than that properly
tanned, but, since this artificial filling is washed out on the first
contact with water and the leather rapidly deteriorates through
attracting and retaining moisture, the fraud of the system is at once
apparent.

Although the use of leather artificially weighted with hygroscopic
chemicals is extremely detrimental to health, it was only during last
year that laws were passed forbidding the adulteration of leather,
and even these are inadequate. Strange to relate, the two countries
where these legal measures have been taken, Australia and South
Africa, enjoy for the most part a hot and dry climate, while it is
in wet weather that adulterated leather is most harmful. However, to
Australia belongs the honour of initiating legal measures against
frauds in leather manufacture, and their praiseworthy action must
soon be copied by other civilised countries.

On the other hand, it would be inadvisable to prohibit the addition
of every other material except those with tanning properties. There
are undoubtedly a few substances which, used in combination with the
tanning materials, add to the strength and value of the leather, and
it is the opinion of some tanners that great developments will take
place in this direction. Certain oils, sulphonated in order to render
them easily miscible with water, and known commercially as "soluble"
oils, exercise a beneficial effect when mixed with the tan liquors,
for they lubricate the fibres of the leather, assist penetration of
and fix the tannin. The time required for the process is, therefore,
much reduced, as strong liquors may be used without harmful effect.
The oil also serves as a lubricant for the fibres, obviates the
harshness and brittleness usually associated with rapidly-tanned
leather, and fixed to the extent of about 3 per cent., must increase
its durability. Best of all, from the tanner's point of view, there
is a moderate increase of weight. There are two or three special
tanning oils on the market.

A vegetable gummy product has lately been introduced to the trade
which has been found to give remarkable results when used in
conjunction with tanning materials. This gummy matter is extracted
from vegetable seeds and is placed on the market under the name of
Tragasol. Its composition is somewhat similar to that of tannins,
the Tragasol Co.'s analysis showing it to contain 43.51 per cent, of
carbon, 6.23 per cent. of hydrogen, 48.38 per cent. of oxygen, 0.39
per cent. of nitrogen, and 1.49 per cent. of ash. It is very largely
used for strengthening and sizing textile fabrics, and seems destined
to play an important part in the leather trade, for it has tanning
properties, increases the strength of the leather, and considerably
hastens the process. Its most important advantage is that it permits
successful tannage in the drum, thus effecting a great saving of time
and labour.

Hitherto, rapid tannages have not been very successful, as they
generally made the leather harsh and brittle, and lessened its
durability. Leather tanned by previous rapid methods was also less
waterproof than that tanned in pits by slow methods. All these
defects are avoided by using Tragasol, which, when combined with
tanning extracts, forms a curdy precipitate, described by the makers
of Tragasol as cutiloid (contraction of cutis and colloid, cutis
meaning "skin," and the Tragasol being, chemically, a colloid). The
cutiloid tannage increases the water-resistant properties of leather,
and prevents the oxidation and consequent darkening of the colour of
the tanning material used with it. Tests have been made which show
that cutiloid-tanned leather will withstand a fall of water 12 in.
high for six weeks before complete penetration takes place; ordinary
tannages do not often resist water for more than a few hours.

For the tannage of sole leather in the drum by the cutiloid process,
about 120 per cent. of Tragasol and 40 per cent. of chestnut or
oakwood extract are required; this quantity is divided into four
equal portions, which are added to the drum successively at intervals
of one hour. The hides should then be nearly tanned through, and the
process is completed with strong extract (chestnut and quebracho,
or myrobalans, according to the kind of leather required). After
drumming the hides for ten hours, they should remain at rest for two
hours, then drummed another hour, and so on, alternately, until the
completion of the process, which may require from twenty-four to
thirty-six hours, according to the substance of the hides. By this
process, the yield of leather may exceed 60 per cent. of the weight
of the raw pelts. This percentage of yield may be raised to 70 per
cent. or more in the case of sole leather by steeping the hides in
hot extract.

The action of acids in swelling gelatine is sometimes abused,
particularly on the Continent and in America. As pointed out before,
tan liquors must be mildly acid in character before the process can
proceed, and, if the organic acids of the tanning materials are
insufficient, the addition of a small quantity of formic, or lactic,
or acetic acid is necessary; but, in many of the American acid
tannages, an excessive quantity of mineral acid is used, with the
object of swelling the hides. When in this condition, they rapidly
absorb an abnormal quantity of tannin, and the finished leather is
unnaturally thick. To make matters worse, the tannage is sometimes
not completed, but, instead, the hides are treated ("doped") with
hygroscopic chemicals, which not only increase the weight of the
leather but also endanger the health of those who have to wear
it. Most of the American tanneries make no secret of their use of
these unnecessary chemicals, but assert that they are obliged to
use them in order to meet competition, and because a large number
of bootmakers insist on buying sole leather at a low price per lb.
The Leather and Paper Department of the U.S.A. Bureau of Industry
analysed several American leathers in 1913 and found that a large
majority were artificially weighted with glucose and Epsom salts
(magnesium sulphate). Barium compounds are also used for the same
purpose, but the American tannages are apparently free of this
adulterant. The results were published in a pamphlet by the United
States Government, together with a list of the firms whose leathers
were tested.

While the European tanners do not weight their leather so freely as
the Americans with these chemicals, the practice of swelling the
hides unduly is not unknown, with the difference that, especially
on the Continent, the swollen fibres are fixed by treating the
hides with a weak solution of formaldehyde, which also acts as a
preliminary tanning agent. The tannage can then be rapidly completed
with fairly strong extracts, as the formaldehyde prevents the
contraction of the grain which would ensue if untreated raw pelts
were placed in strong tan liquor. The acid-formaldehyde process is
risky, and cannot be recommended. The use of the artificial tannin,
neradol, has replaced it in many Continental sole-leather tanneries.
A preliminary tannage with neradol forms a good mordant for the use
of the strong extracts.

  [Illustration: FIG. 26

  PINNING SOLE BUTTS]

Whatever the method used to improve or depreciate the natural
tannage, the surplus material left on the surface is raised or
brushed off, and, after the leather has been left to drain for a
few hours, it is sent to the finishing department, which is usually
the drying shed. There, it is left piled up for a day or two, until
it is in the right condition for oiling. The leather must be oiled,
otherwise the grain would be harsh and brittle when dry, and would
darken in colour, especially at the edges. Cod oil is generally used,
and sometimes a little mineral oil is added to it to prevent possible
impurities in the fish oil rising to the surface of the leather or
causing damage in other ways. A cod oil purified by distillation
would, however, be quite safe to use, and there seems to be no
reason why tanners should use crude oils so frequently as they do,
now that a large number of oils specially prepared for the leather
trade are available. Linseed oil is also used in admixture with cod
oil, its oxidising properties hastening the process of drying. The
leather is liberally oiled with a brush or swab on the grain side and
immediately hung up in the drying shed, where it is left until it
reaches what is technically known as a "sammed" condition (_i.e._,
just damp enough to exude no water when the leather is doubled over).
It is then struck out ("pinned") on the grain side, either with a
hand tool (Fig. 26) or by machine. In the former case, the leather
is placed on a long wooden beam and the pinner works from the left
side, keeping two of the three edges of his knife flat on the leather
while making heavy forward strokes. As the scum is worked out, the
operator mops it up with a wet cloth. Machinery has replaced hand
labour in this operation in all modern tanneries. The pressure of
the tool removes scud and dirt, varying in quantity according to the
amount of "bloom" contained in the particular tanning materials
used. The leather is then laid in pile for a few hours, when it is in
a fit condition for the first rolling, which is known in the trade as
"rolling on." This operation is generally done by machine (Fig. 27)
nowadays, but the old method of using a hand roller heavily weighted
with an iron box (Fig. 28) is still practised in a few yards. After
rolling, the leather is hung up again until nearly dry, when it is
taken down and sized with a weak colouring matter, made up of annatto
or tumeric, with chalk or whitening dissolved in white vinegar
(acetic acid) and diluted. It is then rolled again ("rolling off")
and polished with a piece of flannel. Finally, it is hung up to air
off, and is then ready for the warehouse.

  [Illustration: FIG. 27

  ROLLING MACHINE]

In many yards the finishing consists merely in striking out the
leather, rolling it when properly tempered, hanging up until nearly
dry, and re-rolling. An American machine for giving the final polish
to sole leather has lately been introduced.

Instead of the rolling machine, some French tanners use the hammering
machine, which gives good results, but is necessarily slow and
frightfully noisy in action. The steel hammer moves up and down with
remarkable rapidity, but only a small area is covered by each blow.

  [Illustration: FIG. 28

  OLD METHOD OF ROLLING SOLE LEATHER]

The artificial drying of sole leather, or of any other kind, is a
matter that needs careful attention, for it is obvious that great
delay would occur, and a large amount of business would be lost,
if tanners relied solely on the climatic conditions of the British
Isles; in fact, the weather is so rarely fit for drying leather that
every up-to-date tannery contains some artificial aids, the need
for which has been more pressing since a large proportion of leather
contains a surplus of tanning matter which is liable to oxidise in
contact with strong light and air, thereby darkening the leather and
making it brittle.

Among the satisfactory drying plants are those of Howard-Smith &
Co., and the Sutcliffe Ventilating and Drying Co., Ltd. Both work on
the theory of fanning a continuous current of hot air through the
drying-room, so that the moisture evaporating from the leather is
constantly drawn off while the apparatus is at work.

  [Illustration: FIG. 29

  FAN

  (Howard-Smith system)]

The Howard-Smith plant consists of a series of steel tubes into which
hot water or steam is pumped. These pipes are enclosed in a chamber
in which the air naturally acquires great heat. A fan (Fig. 29) is
fixed in one side of this chamber (Fig. 30) and, when in motion,
drives the hot air through a wide tube which leads to the drying
chamber.

  [Illustration: FIG. 30

  FAN FIXED IN CHAMBER

  (Howard-Smith system)]

Figure 31 shows the Sutcliffe Fan and Heater installed in a tannery.
At least two hygrometers should be hung up in a drying-room to
determine the amount of moisture in the air.


CHROME SOLE LEATHER

The manufacture of chrome sole leather suitable for ordinary walking
boots is of comparatively recent origin, although natural chrome
hides were dressed more than twenty years ago for tennis boot soles
and other athletic shoes. There can be no doubt of the superior
wearing and waterproof qualities of well-dressed chrome sole, but its
high price, compared with that of vegetable-tanned sole leather, is
against its general use.

Either the one bath or two bath tannage (described on p. 108) may be
used, but, on the whole, the one bath method is preferred for the
following reasons: (1) Its application is easier; (2) it produces
a firmer and less elastic leather; and (3) there is practically no
danger of weakening the hide fibres. On the other hand, the two-bath
process produces a plumper leather which can, naturally, carry more
dressing and command a correspondingly better price. In skilled
hands, it is also under better control than the one-bath process,
while it is absolutely necessary for the popular pale bluish-grey
tint of chrome leather tennis soles.

  [Illustration: FIG. 31

  SUTCLIFFE SYSTEM OF DRYING]

The natural chrome sole requires very little dressing. The chromed
hides (usually rounded into butts or bends, shoulders and bellies)
are allowed to remain on a horse two or three days after the
completion of the tannage, so that the oxide of chromium may combine
more firmly with the fibres. They are then placed in the drum
tumbler again and washed in cold water for several hours. A constant
stream is conveyed to the drum through a rubber pipe fixed to the
tap, and escapes through small holes in the drum. The acid salts
are not thoroughly removed by this washing and must, therefore,
be neutralised with an alkali. Borax is the best for the purpose,
owing to its mild action on leather and antiseptic properties. From
1 to 2 per cent. borax on the weight of the leather is generally
sufficient, while, if soda be used for economical reasons, only
half the quantity is required. The drum is revolved for about an
hour; the liquor is then run off, and the leather receives a further
washing in cold water for half an hour, when it is in a condition to
receive the dressing, which is chiefly composed of materials which
help to fill and lubricate the interstices of the fibres so that
the substance is maintained and the natural strength of the fibres
preserved. Gelatine, pure glue, Tragasol, paraffin wax, carnauba wax,
spermaceti, Marseilles soap, are among the various ingredients used;
while the delicacy of the tint may be improved with china clay or
French chalk. Recipes vary considerably, each manufacturer claiming
to have secret methods. Solutions are made of the ingredients, or,
where one or more of the materials are insoluble, they are atomised
in a mixing pan before use. To induce thorough penetration, the
dressing liquid may be applied to the leather at a fairly high
temperature, as chrome leather is unaffected by heat which would
destroy the fibres of ordinary vegetable-tanned leather. Even so, it
is inadvisable to use a higher temperature than 170° F. The leather
is thoroughly impregnated with the dressing in about an hour's time,
and is then piled on a wooden horse for several hours, or overnight,
to drain and permit thorough incorporation of the dressing with the
leather. When well-drained, the grain of the hides is smoothed by
pressure with a special tool (Fig. 32) or by machine, the operation
being known technically as "striking out." The machine (Fig. 34)
gives quite satisfactory results and has replaced hand labour in all
modern works. The hides are then "strained" (_i.e._, extended and
nailed to wooden frames), or they are simply hung up to dry. In the
latter case, there is a small shrinkage of the size of the hide, but
the substance is maintained. With good straining, a satisfactory
increase of surface measurement can be obtained.

  [Illustration: FIG. 32

  SLEEKER]

When the leather is completely dried, it may be sold at once, but
if, as is generally the case, a special "nap" finish is required on
the flesh side, the hides are placed in damped deal sawdust until
they are in the right condition of flexibility for the next process,
known as "fluffing." This is done on a rapidly revolving wheel (Fig.
33) covered with emery powder varying in the size of grain according
to the effect desired on the finished leather. The abrasion of the
leather on the flesh (_i.e._, the under side) raises a soft nap.
Carborundum, a special abrasive made in America, by the fusion of
sand, coke, and salt at a very high temperature, has to some extent
supplanted the use of emery. As a final finish, the flesh side may
be rubbed over with chalk or china clay to give it a clear saleable
appearance.

  [Illustration: FIG. 33

  FLUFFING MACHINE]

The chrome sole leather used for ordinary boots is quite a different
product, and it is only in the last two or three years that it has
been used to any extent. The "Dri-ped" is the best known make of
this leather. The tannage is effected by the one or two-bath methods
already described. The processes preparatory to chroming are very
important, as it is essential to get the maximum yield of pelt. The
hides are, therefore, often treated with sulphide of sodium, which
loosens the hair in twenty-four hours or less. They are then placed
in fairly strong limes for two or three days to swell the fibres and
saponify the grease. After being washed in cold water, the hides are
treated with a weak solution of lactic, boracic, or butyric acid,
or butyrate of ammonia, to remove all trace of lime, when they are
ready to be chrome-tanned. After chroming them, neutralisation of
the acid chrome salts is effected with borax, and the leather is
ready for dressing. The principal objects of this process are to
make the leather firm and waterproof, and to remedy its tendency
to slip easily on wet pavements. The last-named is the greatest
difficulty, and there are only about two or three firms who have
really surmounted it. Each manufacturer keeps his recipe secret, but
the ingredients that go to make the various dressings are drawn from
the following: Stearines, mineral oil, Tragasol, resin, carnauba
wax, beeswax, paraffin wax, glue. Resin, or asphalt, or both, may be
used to prevent the leather slipping in contact with a wet pavement.
One patent describes a method of dressing chrome sole leather with a
mixture of asphalt, resin, and paraffin wax.

  [Illustration: FIG. 34

  STRIKING-OUT AND SCOURING MACHINE]

The waterproofing ingredients are preferably applied to the leather
in the tumbler at a high temperature, say, 160-170° F. After
running the drum for about three-quarters of an hour, the leather
is impregnated with the mixture, and is then horsed up for at least
twenty-four hours to allow complete incorporation of the fatty
ingredients with the fibres of the leather. A suitable waterproof
dressing and filling increases the strength of the leather.

The finishing of the leather is simple. The butts or bends are
smoothed and stretched out by machine (Fig. 34), oiled on the grain,
nailed or extended with special metal grips on square wooden frames,
and dried. In some cases, they are hung up until nearly dry, rolled
by machine instead of being put on boards and aired off in a drying
stove.

A patented method of making waterproof chrome sole leather to
prevent it slipping and losing its shape in wear consists in first
treating the leather in a solution of glue, gelatine, agar-agar,
or other colloidal substance, with the addition of formaldehyde,
and then submitting it to strong pressure under the influence of
a high temperature, in order to fix the colloidal matters. The
pressure is made between heated plates. The leather is afterwards
impregnated with a mixture of wool-grease, pitch, asphalt, resin,
wax, gutta-percha, etc. A recipe given in the specification consists
of wool grease (60 parts), asphalt (10 parts), soft pitch (25 parts)
and gutta-percha (5 parts). The mass is fused and kept at 90° C. The
hides are placed flat in this mixture, which they quickly absorb.

If the British Government should ever introduce a Bill to stop the
adulteration of leather, it may be found somewhat difficult to deal
with chrome sole, which must have some filling material to make its
use practicable. No exception can be taken to the dressing of leather
with materials that make it waterproof and increase its strength; in
fact, much more will be done in this direction than has ever been
attempted in the past, as waterproof sole leather is a necessity in
Great Britain. Any measure to check the adulteration of leather must,
therefore, clearly define the chemicals which are known to be harmful
in leather and which may not be used. This has not been overlooked
by the Australian Government, which has forbidden the use of barium
salts in leather, and likewise the importation of leather boots or
any goods made of leather containing this chemical. Such goods sent
to Australia are liable to confiscation, and it is reported that a
few consignments of boots have already been condemned.

Leather, either exported or imported, must not contain more than
3 per cent. of glucose unless the percentage is marked on each
consignment, in which case, it is presumed, a tanner may use as
much of the adulterant as he likes, although the fact that he
has to disclose this practice acts as a deterrent in most cases.
Unfortunately, the Australian Act leaves an important loophole, since
the use of Epsom salts, which can be made to increase the weight of
leather more than any other chemical, is not prohibited. In any case,
none of these hygroscopic materials is of any use to chrome sole, for
they would attract moisture which it is desirable to resist.


VACHE SOLE LEATHER

As its name implies, vache sole leather is a Continental product,
being made chiefly in France, Belgium, and Germany. The raw material
consists of light and medium cow hides. The details of working are
somewhat similar to those used in tanning English sole leather,
the main difference being that the hides are suspended in the lime
liquors instead of throwing them in flat. The system of tannage is
not so varied as the English, since the materials used generally
consist of oak and pine barks, myrobalans, quebracho and oak
extracts; and the finishing materials are of quite another character.
The Continental tanners generally use the Réaumur thermometer, while
the Beaumé hydrometer is used to determine the density of the tan
liquors in place of the English barkometer (Fig. 24). One degree
Beaumé is equal to 6.9° barkometer.

Vache leather is more pliable than English sole leather, but the
addition of valonia extract towards the end of the tanning process
would greatly increase its firmness.

The finish is applied to the flesh side of the leather, and a typical
recipe consists of a size such as Irish moss or Tragasol (1 part),
flour (20 parts), china clay (20 parts), and pure gambier (2 parts)
in 200 parts of water. The size is dissolved and cooled, and the
other ingredients are then added.


MACHINE BELTING, HARNESS, AND SADDLERY LEATHERS

These leathers are rarely made by one firm; usually, strap butts and
most kinds of belting leathers are dressed by curriers, whose trade
is quite distinct from that of currying shoe leather. The tanning and
currying of harness and saddlery leathers is another special branch.
Besides these three important trades, there is the dressing of
hydraulic, mechanical, and other industrial leathers, which likewise
form special sections of the heavy leather industry.

Belting leather is an important item in the trade, and, as a good
proportion is made from the finest hides, this class of leather is
among the most expensive made. At present, there is much controversy
in the trade as to whether the vegetable-tanned or the chrome-tanned
article is the more economical in use. Briefly, chrome belting is
superior in works where there is much steam or mineral acids, as it
is not affected by these conditions to the same extent as bark-tanned
belting. Its tensile strength is also greater, but against these
advantages must be set its higher cost and tendency to stretch
unduly in comparison with the vegetable-tanned product. It can be
safely said, however, that the use of chrome belting is on the
increase, although its production is not nearly on such a big scale
as that of the old type of belting.

The tannage of belting leather is similar to that of sole leather,
except that there is no necessity to continue the process, after the
tannin has struck through, with the object of increasing its firmness
and weight. Attention must also be paid to the class of tanning
materials used, especially for belting of the best quality, as it
must have great tensile strength and stand a severe strain in the
dynamometric test. Tannins that rapidly oxidise in contact with light
and air have, therefore, to be avoided. The oak bark tannage, with
a little chestnut and oakwood extracts to finish the process, is a
good method of imparting to the hide the right degree of firmness and
flexibility.

As in the case of sole leather, belting may be artificially weighted
during the tannage, although it is usually done in the currying
process, if at all. There can be no doubt that a quantity of
adulterated belting leather is made, and will continue to be made
while the practice of selling by weight is in vogue. As a rule,
sophisticated belting leather has a much weaker tensile strength than
the pure product and is of relatively poor value, since the reduction
of price is usually a matter of only a few pence. If users of belting
bought on the principle of value instead of price, they would never
buy adulterated leather.

  [Illustration: FIG. 35

  LEATHER-STUFFING DRUM]

In tanning hides for belting, the shoulders and bellies are cut off
and usually dressed for sole or harness leather, leaving the butt,
the prime part of the hide, 4-1/2 ft. in length (Fig. 23). The
tanned butt is first shaved to level the substance, then washed in
a solution of borax, and sumached in the drum. After smoothing the
leather in the striking-out machine, it is partially dried ("sammed")
and then rubbed on both sides with a dubbin of cod oil and tallow. In
this condition the butts are left piled up for a few days, so that
the dubbin penetrates the leather, which is then extended with the
sleeker (Fig. 32) to make it smooth and to remove surplus grease,
which is sold to soap-makers under the currier's name of "moisings."
The leather is finally dried, rolled (optional), stretched by
machine, and cut up in the width of belting required. Instead of
"hand-stuffing" the leather with cod oil and tallow, which is still
the best method, a large quantity of butts are now "drum-stuffed,"
the object being to make use of stearines, which are harder and
heavier greases than tallow. The type of drum shown in Figure 35, in
which the grease is incorporated with the leather by means of live
steam, gives satisfactory results, although hot air apparatus is now
replacing the steam injector.

A patent has lately been granted to an American inventor for the
production of a strong and cheap belting. Flesh splits of hides are
simply stuck together with a collodion or nitrocellulose solution.
Any number of layers may be used, according to the substance
required, the only essential quality being that the leather should
be free from grease. The adhesive property of nitrocellulose
solutions is probably stronger than that of any other material, but,
unfortunately, the tough film they form on drying does not grip
a greasy surface. Before the solution used to join the pieces of
leather together is dry, the leather is rolled under heavy pressure,
and, when thoroughly dried, can be cut up for belting.

The dressing of harness leather is similar to the manual process of
making belting, with the exception that the butts or bends (half
butts) are stained either black or a pale straw colour, the latter
being known to the trade as the "London colour." Annatto is often
used to get this colour. The bright, greasy finish on harness leather
is obtained by rubbing buck tallow over the grain and polishing with
a glass sleeker or a piece of flannel. The operation is sometimes
done by machine, in which the working cylinder is covered with pieces
of cotton rag.

Saddlery leathers are dressed on similar lines, but the finish is not
so greasy as harness. Pig skins make the best and toughest leather
for this purpose. They are dressed in a similar manner to harness
hides, but special attention has to be given to pig skins to get rid
of the large quantity of natural grease they contain.


BOOT UPPER LEATHERS

Whereas the number of different kinds of boot upper leathers in use
less than three decades ago was limited to five or six (waxed calf,
calf kid, French kid, mock kid, levant, coloured calf) it is now
almost legion. Although the variety is almost bewildering, however,
the popular demand is confined to about half-a-dozen sorts, which
include real and imitation box calf, box hide, _glacé_ or glazed kid,
patent leather, willow calf, dull-finished chrome leather, and waxed
kip butts and waxed splits for workmen's boots.

Box leathers and glazed kid are the most popular of all. Generally
speaking, glazed kid is more suitable for wear in the summer and
autumn; while box leather, being thicker and stronger, is preferable
for the winter. Imitation willow calf (_i.e._, calf skin tanned in
vegetable and chrome liquors, either separately or combined) is very
suitable for easy-wearing boots, but is not so durable and resistant
to water as the pure chrome-tanned article.

The tannage of box and willow leathers may be effected by the one
or two-bath process already described (p. 108). Before the tannage,
it is advisable to pickle the hides or skins in a solution of alum
and salt, with the object of preventing contraction of the tissues
of the hide, and providing a mordant for the more rapid absorption
and fixation of the chrome salts. The tannage completed, the acid
salts in the leathers are neutralised with borax, and after the
leather has been washed in warm water it is ready for dyeing. The
dyeing of box calf is generally done in the drum tumbler, but there
are several other methods. One system used on the Continent is to
dip the skins, a pair at a time and placed flesh to flesh, in a very
strong dye liquor. This method is slow, and not in accordance with
modern ideas; used for producing browns and fancy shades, it is very
difficult to avoid irregularity of colour where large parcels are
manipulated. Another method is vat dyeing, the process being carried
out in a wooden vat (Fig. 25) and the dye liquor circulated by means
of a paddle. The one advantage of this system is that the leather
can be easily examined during the process. A useful method of dyeing
is carried out by brushing the colouring materials on the grain side
of the leather. This process is economical, and it has the further
advantage that the finished leather can be used for unlined boots and
other purposes where an undyed flesh is necessary.

The original "box" leather was dyed a dark-blue shade in the drum
before it was shaved, and, as the dye does not penetrate very far
into chrome leather, unless a strong mordant of tannin be previously
used, the subsequent shaving left the flesh side of the leather a
very pale-bluish tint.

The process of dyeing is least troublesome and most effective when
done in the drum tumbler. The leather is run in warm water until the
temperature reaches 140°-150° F (60°-66° C.) and the dyeing materials
are added gradually in a box at the side of the drum whence it passes
through the axle or journal into the tumbler. Although chrome leather
is not materially affected by boiling water in contradistinction
to vegetable-tanned leather, which cannot be treated with water
above 60° C. without injury, it is inadvisable to dye it in
boiling solutions, the above-mentioned temperature being the most
satisfactory. There are two methods of dyeing blacks in the leather
trade: (1) the logwood-ammonia, and (2) the aniline black. The former
is the cheaper of the two and quite satisfactory, although many
dyers seem to prefer the aniline process. The latter certainly gives
a deeper black, but it is not at all necessary to make the flesh side
of box calf black, and many buyers prefer the back blue, although, of
course, the grain side of the leather must be finished a jet black.
The crude logwood is generally subjected to a process of fermentation
or "ageing." The new wood has to be placed on stone or cemented
flooring in a warm room and frequently turned over until fermentation
has ceased, which usually takes about a week. It is then cut into
small chips by machinery and packed in bags. This is the form in
which it always used to enter the tannery, but it is now generally
prepared in paste or crystal extract by makers of tanning and
dye-wood extracts, a business which grows in importance every year.
The colouring matter of logwood is haematoxylin, which is converted
into haematin by oxidation; hence, the extract is often referred to
as haematin crystals. The paste may be used where it is desirable
to increase the substance of the leather, but most dyers prefer
the crystals, which are easily dissolved in hot water. One lb. of
crystals, to which is added just enough ammonia to change the brown
colour to violet blue, suffices for each 100 lb. of leather dyed. The
colouring matter is absorbed by the time the drum has been running
half an hour, leaving clear water behind. The next process is known
technically as "fat-liquoring," which, as its name implies, consists
in lubricating the fibres of the leather with fatty or oily matters.
This is a very important process, for, when suitable ingredients
are used, the pliability, strength, and waterproof quality of the
leather are greatly increased. The making of special fat-liquors for
different kinds of leather has become quite an important business,
and most makes can be depended upon for the specified purposes. It
is a debatable point as to whether fat-liquoring should precede or
follow dyeing. Generally speaking, it is better to adopt the latter
course, as the fatty ingredients help to fix the colouring matter on
the fibres of the leather. The dye is also less liable to fade when
fat liquoring follows the colouring.

The number of materials that may be used for the process of
fat-liquoring is almost legion, but the principal are soaps, oils,
egg-yolk, tallow, flour, Tragasol, Irish moss, china clay, and
starch. Unless the special preparations made by leather trade
chemical firms be used, much care has to be exercised in selecting
the most suitable ingredients for each class of leather. For example,
the mixture that would give good results on vegetable-tanned leather
might be quite unsuitable for chrome leather. Then, again, the
selection of material is based on the style of finish required, a
dull finish necessitating heavy fats and greases which would be
quite unsuitable for bright leathers, and particularly for those of
the chrome-tannage. Among the hundreds of recipes that have been
published from time to time, tallow has only found a place in one or
two mixtures, yet it is one of the finest materials for strengthening
and lubricating the fibres of leather. If its splendid properties
were fully known, it would be very largely used for fat-liquoring
purposes. Of course, it is well known to the currying trade, having
for several centuries formed the basis, together with cod oil, of the
dubbin used in stuffing waxed leather and belting butts.

The following is a useful recipe for a fat-liquor for box calf: 2 lb.
Marseilles soap and 3 lb. neatsfoot oil for every 100 lb. of leather.
The soap is cut into small pieces and dissolved in hot water, and
the oil is added slowly and thoroughly mixed by stirring vigorously.
Where possible, emulsification should be done in a machine, in order
to atomise the ingredients. The finer they can be brought into a
state of division, the better they will be absorbed by the leather.
Other suitable fat-liquors for box leathers are the following: (1)
Turkey red oil, 2 per cent. of weight of leather and neutral soap 1
per cent.: (2) neatsfoot oil, 2 lb.; tallow, 1 lb.; and Tragasol,
1 lb.: (3) cod oil, 2 lbs.; Marseilles soap, 1 lb.: (4) neatsfoot
oil, 2 lbs.; egg-yolk, 1/2 lb., or six fresh yolks. The process is
completed in 20-30 minutes.

In the case of fancy colours or browns, the leather should generally
be well-drained and warmed up again in the drum in hot water (170°
F.) before fat-liquoring, but the precaution is unnecessary for
black leathers. After the fat-liquoring process, the leather is
removed from the drum, and piled up on the horse to drain, and left
for several hours or overnight, to allow it to assimilate the fatty
ingredients. It is then submitted to an operation known as sleeking
or striking out, with the object of removing surplus water and so
facilitating drying, and making the grain side smooth. Machinery is
now almost universally employed, especially for chrome leather. A
good type of striking out machine is shown in Figure 34.

If done by hand, the skins are placed on a sloping glass or slate
table, with the flesh side uppermost, which is then stretched out by
strong pressure with a tool known as a sleeker, the strokes being
made downward in the direction of the hair growth. The flesh side
done, the whole skin is turned over and the grain side is similarly
treated. Sometimes only the flesh side is struck out, especially
if the grain is soft and tender. The sleeker consists of an iron,
steel, or copper blade, about 6 in. square, fitted in a wood handle
(Fig. 32). The skins are hung up in the drying-room immediately they
are extended and smoothed by sleeking, and are then either allowed
to dry completely, or, as is generally the case with best leather,
they are hung up until a great deal of the moisture is evaporated
and the skins are left in a slightly moist, or, as it is generally
termed, "sammed" condition. The skins are then taken down, damped in
dry parts, folded over, laid in piles to equalise the moisture, and
finally smoothed out and stretched again by hand or machine. This
second operation after the dyeing is known as "setting."

Chrome-tanned skins are usually stretched and nailed on square boards
after setting, as, owing to their elasticity, they are liable to
shrink considerably in drying. The superficial area can be increased
by fully extending the skins. This operation is technically described
as "straining." It may be stated here that vegetable-tanned leathers
are not generally "strained" on boards, as such leather is better in
quality and substance when hung up and dried. Leather of combined
tannage (_i.e._, tanned with vegetable and chrome products) is,
however, frequently "strained," as the astringent property of chrome
would otherwise cause contraction of the fibres.

When dried on the boards the leather is somewhat stiff, and has,
therefore, to be softened before any finishing ingredients are
applied. Chrome leather is softened by placing it for a few days in
damp sawdust, which, for brown or fancy coloured leather, must be of
deal or white pine, and, therefore, free from objectionable colouring
matter; but, for black leather, the sawdust of any wood is suitable.
The skins must be systematically piled one above the other, and a
little damped sawdust scattered over each skin.

When properly "seasoned," the skins are brushed free of the sawdust
and "staked," either by hand or machine, usually by the latter
means. The staking knife may be fixed in a wood crutch (arm stake),
or fixed upright in a vertical wooden stand (knee stake). In the
former case, the skins to be staked must be secured in a horizontal
wooden groove fixed to two uprights, the workman then pressing
heavily in a downward direction with the staking knife, of which the
crutch is held under the armpit. In using the upright stake, the
leather is moved to and fro over the edge of the fixed knife. Both
of these manual operations are arduous and somewhat dangerous, and
should be displaced by machinery wherever possible (Fig. 36).

  [Illustration: FIG. 36

  STAKING AND GLAZING MACHINE]

The thoroughly softened leather is then dried, mordanted with a
solution of logwood, or haematin crystals, blacked with levant ink,
a specially prepared black dye, or with a suitable aniline dye, and
dried again. It is finally seasoned with a glutinous or albuminous
mixture (blood albumen, milk, and a little aniline black dye make a
good mixture), dried, glazed, seasoned a second time, and reglazed.
A light coating of mineral oil turns the finish into a jet black,
and the leather is ready for the warehouse. There are several types
of glazing machines, but the "grasshopper" (so called owing to its
action) is the most popular for box calf. This machine is the same as
shown in Figure 36, except that the working tool is replaced with a
smooth glass or agate roller.

The term "box" applied to this leather was invented by a prominent
American tanner, and had he registered the name and patented his
process he would have reaped a very rich harvest, for the leather
is used in enormous quantities throughout the world. As it was, the
American firm tried to obtain an injunction against English firms
manufacturing the leather, but had to withdraw their claim, as they
were not the inventors of chrome leather, which was made in Scotland
before it was introduced to the States. Moreover, the word "box," as
applied to leather, was not registered in the United Kingdom.

Willow calf is exactly the same kind of leather as box calf, except
that it is dyed brown instead of black. The seasoning mixture
naturally differs and may consist of a mixture of egg albumen, milk,
and a little of the same, or similar, dye solution as that used in
the dyeing process. In order to get clear colouring, the dyes should
be well dissolved and strained through fine muslin.


CHAMOIS LEATHER

This kind of leather is well known to the general public under the
name of wash-leather, but it is, perhaps, not so widely known that
there is practically no real chamois leather available, since the
species of animal bearing this name is almost extinct. Nowadays,
"chamois," or "shamoy" is made from the flesh split of sheep skin,
and the method whereby the leather is produced is described as the
oil tannage. The chamois leather dresser may also do the preliminary
work of fellmongering, but more often he receives the pelts, or
"fells," from the fellmonger. Although the pelts have been in a lime
liquor known as the fellmonger's "gathering limes," the process of
liming has to be continued and carefully regulated. Too much liming
makes the pelts loose, owing to the development of bacteria. This
effect would cause the finished leather to be soft and spongy. On the
other hand, under-liming fails to remove sufficient of the cement
substance which binds the fibres of the pelts; consequently, the
leather produced from these pelts is thin and somewhat gristly. After
being limed, the skins are "cobbed" (_i.e._, the bits of wool or hair
left on by the fellmonger are removed) and the pelts are then fleshed
by machinery. The next operation, splitting, is very important and
requires skilful attention to get good results. The Reeder machine
is largely in use, but the band-knife machine is also suitable. The
top half of the sheep skin (_i.e._, the grain side) is utilised for
the manufacture of skivers, while the under portion, or flesh side,
technically called "lining," serves as the raw material for chamois
leather. The best linings are generally sorted out for making into
parchment, which, of course, commands a much higher price than
chamois. Linings for chamois are then submitted to the operation of
either re-splitting or frizing, the object being to remove the loose
tissue lying between the grain and flesh. The pelts are re-split in
the case of cheap chamois, but frized if intended for choice finish.
Frizing is an operation peculiar to the making of chamois and glove
leather. It is done with a very sharp knife, similar to the fleshing
knife, and on a more upright beam than that used by tanners. The work
requires great skill, frizers being among the best paid workers in
the trade. Frizing done, the linings are freed from lime by washing
them in the drum tumbler, or paddle-vat, through which cold water is
allowed to flow continuously for two or three hours. When lamb skins,
which are too thin to split, are made into chamois leather, the grain
is removed by frizing.

A quick and effective method of deliming is to treat the skins
in a weak solution of lactic acid. Some dressers use a drench of
pea-flour or bran. The mild acids produced by the fermentation of
these materials not only neutralise the lime but also reduce the
gristly nature of the skins to a soft, supple condition. The bran
infusion is slightly warmed to hasten the process of fermentation,
but the temperature must not exceed 100° F. (32° C.). The linings
are then rinsed in cold water and sent to the stocking machines,
in which they are kneaded until they become quite soft. Either the
faller-stocks or the mechanical pushers (Fig. 14) may be used, the
latter being the more modern machine. The operation may require from
four to ten hours, the completion being determined by the condition
of the skins. "Samming" follows stocking, and for this purpose the
linings are hung up in the drying shed until thoroughly dripped, but
not dried. In this slightly damp condition they are then prepared
for the next process of oiling, which is the most important part of
chamois-dressing, as it converts the perishable raw linings into
leather. In the United Kingdom, cod oil (generally Newfoundland) is
used exclusively, and gives best results. Whale and shark liver, or
menhaden oils are often used abroad.

The linings are placed in a tub or vat, a few at a time, and oil is
poured over each layer until a sufficient number has been treated
to fill the stocking machine. The stocks are run for half-an-hour,
or until the oil has penetrated the linings, when they are put
back into the vat, where they remain for about an hour. They are
then re-stocked, taken into the shed to samm, re-oiled in the vat,
and stocked again. These processes are repeated until the skins
are thoroughly impregnated with the oil, when they are dried in a
warm stove. The skins are not yet converted into leather, which
only occurs in oil-dressing, after the oxidation of the oil. This
is effected by spontaneous heat, the dry oiled skins being heaped
in boxes and covered. Strict attention has to be paid to avoid
over-heating the skins, which are turned over and changed at
intervals. When the leather ceases to heat, the process is completed.
It is then dipped into hot water and mechanically pressed, to remove
surplus or uncombined oil, which is collected and sold under the
name of "sod oil." The leather is afterwards drummed in warm water
and finely cleansed in an alkaline solution, potash, soda, or borax,
chiefly the first named, being used for this purpose. They are then
rinsed in water, dried, damped, and softened by staking. At this
stage, the best skins are sorted out for the glove makers. The
others are finished for wash-leather by re-staking, paring with the
moon-knife, and smoothing both sides of the skin with a scurfer, or
fine pumice-stone. In the warehouse, they are damped, stretched out,
piled up, and kept fully extended by placing heavy weights near the
edges of each pile of skins.


GLOVING LEATHER

Progress in the art of making leather for gloves has been rapid
during the last few years; but further important developments are
expected, particularly in the process of tanning. Practically the
only method that has been used for many decades for converting kid,
lamb, and sheep skins into gloving leather is that known technically
as "tawing," which consists of treating skins with alum, salt,
egg-yolk, flour, and a vegetable oil. These substances change skins
into extremely supple and "stretchy" leather, but when this is
made into gloves it is far from ideal in wear, because it fails
to keep the hands warm in cold, wet weather, it is easily soiled
and cannot be cleaned without great expense, and it is not very
strong in texture. Combination tannages have lately been produced,
however, which remove the defects of alumed leather. By means of a
light chrome tannage after tawing, the leather is strengthened and
made more resistant to water, and can be cleaned with a damp rag
or sponge. By tanning skins with the formaldehyde process, or with
Neradol, the artificial tannin, for making into suède leather, the
finished article is not only washable but also resists the action
of alkalies and soap. The adaptation of combined tannages in the
manufacture of gloving leathers has only lately been developed, and
further improvements will doubtless be effected before long.

Lamb, kid, goat, and sheep skins constitute the raw material for
gloving leathers, although deer and antelope skins are also used
to a small extent. Real kid skins are the best wearing dress
gloves, but the great majority of so-called "kid" gloves are made
of lamb skins. The raw kid and lamb skins are chiefly of European,
Arabian, and Indian origin. Sheep skins from the Cape provide the
raw material for a large number of men's gloves, and leather of
very good quality can be produced from the best grades. Most of the
skins are preserved by drying, or by salting and drying, although
some kid skins are wet-salted and packed in barrels for export. It
would save leather-dressers a great deal of trouble if they could
always get wet-salted skins; but the object of drying them is to
reduce the weight and lower the cost of freight. Soaking is done by
methods already described (p. 65). Loose flesh and pieces of fat
are cut off in order to facilitate the action of the depilitant,
of which the best for glove leather is undoubtedly a paste of lime
and red arsenic. Seven or eight parts of lime to one of arsenic is
a satisfactory proportion, the quantities to be mixed depending on
the number of skins to be treated, as a fresh mixture should be made
for each lot, or "pack" as the tanner terms it. The lime should be
well broken up, or, better still, pure powdered lime should be used
and the red arsenic well mixed with it; a little water is then added
to slake the lime gradually, and the mixture is stirred to promote
chemical reaction. The compound is further diluted with water until
it has the right consistency and the colour has changed. The reaction
generates great heat, and the "paint" should, therefore, not be used
at once. The flesh side is mopped with the paint and the skins are
folded flesh to flesh. After a few hours, or as soon as the hair
or wool is loosened, the skins are dehaired or dewoolled. The hair
or wool is not allowed to come into contact with the depilitant,
otherwise it would be damaged. In large yards, the white hair is
separated from the coloured, as it is worth nearly twice as much.
Wool is sorted into different qualities, of which the number may vary
from four to eight, or even nine, according to the class of skins
treated. The pelts are then thoroughly washed and placed in lime
liquors, where they remain for one or two weeks, being hauled and set
in the usual manner. Fleshing and piecing or trimming are the next
operations, and then follows the very important process of puering,
which, in the case of glove leather, must be thoroughly done so as to
reduce the pelts to a very soft and flaccid condition. Success in the
making of glove leather depends largely on the "puering" process.

In most of the English tanneries a decoction of dog manure is used,
at a temperature not exceeding 90° F., but on the Continent the
artificial puer, oropon, is preferred. It is much safer to use and
more uniform in its action than excrement, which develops bacteria
rapidly in contact with gelatinous pelts, and could ultimately
destroy them entirely. After puering them, the pelts are well washed
and submitted to the process of drenching, which consists in putting
the skins into a warm infusion of bran or pea-flour and leaving them
covered until the following morning. The slightly acid fermentation
causes the pelts to rise to the top of the vat. They are pushed into
the liquor again with a pole and stirred round. This is repeated
three or four times to prevent damage to the grain. The process is
often done in the paddle-vat (Fig. 25), in which the bran liquor is
circulated for several hours before the pelts are allowed to remain
quiescent. Drenching thoroughly purges the pelts of the last traces
of lime, and puts them in suitable condition for being made into
leather. The pelts are then rinsed in tepid water and "scudded" on
the grain with a slate or vulcanite tool, shaped somewhat like a
dehairing knife. The scud removed consists of dirt, dissolved lime
salts, short hairs, and pigment. Machines are rapidly replacing
manual labour for this operation.

The alum tannage, known technically as "tawing," is largely used for
kid and lamb gloves. The tawing mixture is composed of alum, salt,
egg-yolk, and wheaten flour. The proportions used vary considerably
in different tanneries, but the following is a typical recipe: 4 lb.
alum, 2 lb. salt, 1 lb. salted egg-yolk, or the yolks of twenty fresh
eggs, and 5 lb. flour for 100 lb. of pelts. The flour is made into
a paste, the egg yolk is diluted in warm water and mixed with the
flour, the salt and alum are dissolved and added, and the mixture
thoroughly stirred. A suitable quantity of water (about 2 gals. per
100 lb. pelts) is then placed in the drum tumbler, the tawing mixture
is added, and the drum revolved for a few minutes before putting the
pelts in. The process is completed in two or three hours in the case
of thin skins. It is a good plan, however, to leave them at rest
in the drum for a day, after which they are piled up overnight to
allow further combination of the tawing materials with the fibres
of the pelts. The leather is then dried out completely, damped in
clean sawdust, or by sprinkling with water, levelled by shaving if
necessary, staked over an upright knife fixed in a wooden stand
or by machine, and dried in a hot stove. In this condition, or in
the "crust," as dressers term it, the leather is allowed to remain
several weeks to "age," a most essential process for the production
of soft, and supple glove leather.

Dressing and dyeing are begun as soon as the leather is
satisfactorily aged. The skins are uniformly soaked in warm water,
dyed, and re-dressed with egg yolk ("re-egged"), to which a small
quantity of olive oil, or a sulphonated oil, is added. Some dressers
prefer to give the second tawing mixture before dyeing, but the
advantage of dressing the leather after dyeing is that the colour is
securely fixed. In "re-egging," many dressers use a similar mixture
to the first dressing. The dyeing process is of great importance,
since the colour must be fast. The leather is dyed either in the
drum or on a convex table. In the former case, the leather is
naturally coloured both sides, while, in the latter, it is stained
with a brush on the grain side only. Staining is the more difficult
method. Kid glove leather may be dyed with aniline colours, or,
as more generally practised, with natural dye-woods as a base and
aniline dye for top-colouring. The great advantages of the latter
method are economy in dye-stuffs and increased depth of colour. The
skins are first prepared for dyeing by brushing with, or drumming
them in, an alkaline solution. Stale urine was largely used for this
process, but ammonical salts are now generally preferred, if only
for sanitary reasons. The skins are then drummed or paddled in, or
brushed with, dye-wood liquids which have been carefully strained. A
large selection is available, including fustic, cuba wood, saffron,
peachwood, logwood, sappan wood, cutch, Persian berries, gambier or
terra japonica, and golden tan bark.

Light and medium brown can be obtained from these dye-woods without
the aid of aniline colours; but for dark shades, and to increase the
brilliancy of other colours, a top dye or coal-tar dye is often given.

The natural dyes are further developed with "strikers," which mainly
consist of metallic salts. Iron, copper, and zinc sulphates, nitrate
and acetate of iron, bichromate of potash, and titanium salts
(titanium lactate, titanium potassium oxalate, and tanno-titanium
oxalate) are the most important. The lactate, sold commercially under
the name of "corichrome," is especially suitable, as, unlike the
mineral acid salts, especially the sulphates, it has no destructive
effect on the fibres of the leather.

Dye-woods are now concentrated in the form of a paste, or dry
extract, the latter being the more reliable. They are also very
convenient to use and dissolve, while mixtures are, of course,
easily prepared. A good tan shade on Cape sheep can be obtained by
mordanting the leather with a solution of 1 lb. of bichromate of
potash for every 100 lb. of leather, drumming it in 8-9 lb. of pure
gambier, and then with a mixture of cuba wood extract, 1 lb.; fustic
extract, 3/4 lb.; Brazil wood extract, 1/2 lb.; and logwood extract,
1/2 oz. After drumming the leather in this dye liquor for about an
hour, the colour is developed with corichrome. If a darker shade be
required, the leather can be treated with a suitable basic dye. After
dyeing the leather, some dressers only fat-liquor it with egg-yolk
and a small quantity of olive oil, while others prefer to re-dress it
with a similar mixture to that used for tawing, namely, alum, salt,
egg-yolk, and flour; but, where titanium salts are used, the latter
method is not essential, because titanium has tanning properties.
When dry, the leather is ready for finishing, but it is advisable to
keep it in store for a few days before packing it in damp sawdust or
sprinkling it with water to prepare it for the operation of staking.
Anything more unlike leather would be difficult to imagine at this
stage, but, after stretching the skin in the staking machine, or by
drawing it over the upright stake, the dry, stiff, and shrivelled
leather is reduced to a very supple condition. The flesh side of the
leather is then pared with the moon-knife, or in the shaving machine,
to equalise the thickness. In some works, a special tool which pares
the leather on a flat table is preferred; this particular operation
is called "doling." The flesh side is finished by fluffing it on the
emery or carborundum wheel (Fig. 33). Finally, the grain is brushed
and polished with the glass sleeker, or ironed.

Chamois leather has been largely used for gloves of late years,
but this leather has the defect, in common with suède leathers,
of getting soiled much more quickly than grain leathers, such as
kid, lamb, or Cape sheep. Nevertheless, suède and chamois gloves
are likely to remain fashionable to a more or less extent. The
manufacture of chamois leather is described on page 144. Sun-bleached
skins are the best for dyeing, especially if delicate shades are
wanted. The frontispiece shows a field covered with skins bleaching
in the sun. Chemically bleached leather is likely to become
discoloured after dyeing. Defective skins are often dyed with
pigments (dust colours), and this system is also applied to skins
which have to be dyed such delicate shades as cannot be produced by
wood or aniline colours. Although it gives attractive results to the
eye, and certainly covers up any defects of the grain, this method
of dyeing is not altogether satisfactory, as the leather remains
unpleasantly dusty in wear for quite a long time.

The dyeing of chamois with wood-dyes or coal-tar colours is by no
means easy, but this method gives the best results when successful.
The grease must first be removed from the leather with a solution of
5 lb. of borax or 3-1/2 lb. of soda for every 100 lb. of leather.
If the leather is still greasy on the surface, a further quantity
of soda or borax is given, after which the leather is well washed
in warm water, sumached, rinsed to remove the particles of sumach,
and mordanted with titanium salts. The dyeing is then done with
anilines or wood-dyes, or a combination of both, and this is followed
by fat-liquoring with egg-yolk and a sulphonated oil. The finishing
operations are staking and fluffing.

To get a good, fast black on chamois and suède leathers is one
of the difficult processes in the leather trade, although it is
easier to get a good black on alumed or chromed leather than on
vegetable-tanned. Alumed leather is washed in a solution of borax
or carbonate of ammonia to remove uncombined dressing in order to
prepare it for dyeing. Chrome-tanned suède leather does not need this
preparation. The leather is first mordanted with dye-wood extract,
of which a suitable mixture is logwood and fustic, or logwood and
quercitron, in the proportion of 4 lb. and 2 lb. to every 100 lb. of
leather. After drumming the leather in this solution for about an
hour, a weak solution of copperas (ferrous sulphate) and bluestone
(copper sulphate) is added, and the milling is continued for twenty
minutes, when the leather is well prepared to receive the black dye.
Instead of the iron and copper salts, corichrome is often preferred,
as it is quite safe to use, whereas iron salts have a destructive
action on the fibres of the leather, unless the precaution be taken
to mordant the skins with a good quantity of dye-wood extract.
Following the application of the iron or corichrome striker, the
leather is dyed with suitable aniline black (leather black, or
corvoline) and finally fat-liquored to nourish the leather, and to
fix and intensify the black. This recipe also gives good results
where the skins are dyed only on the flesh side, the solutions being
applied with a brush.


WHITE WASHABLE LEATHER

Among the new kinds of leather for gloves, none is more remarkable
or more useful than the washable sheep or goat skins. The great
advantage of this leather is that it can be washed in warm water
and soap any number of times without injury, whereas gloves of
ordinary tawed kid and lamb skins have to be dry cleaned and cannot
be renovated many times. An additional advantage of washable leather
is its warmth. After being dehaired, puered and drenched, the skins
are drummed in a solution of formaldehyde and soda. In two or three
hours, the skins are tanned, and are then treated with a solution
of sulphate of ammonia. The quantities required are about 3 lb. of
formaldehyde (40 per cent.) and 8 lb. of sodium carbonate (80 per
cent.), and 1 lb. of sulphate for 100 lb. of pelts, using sufficient
water to cover the skins well in the drum. This tannage produces a
white but somewhat thin and empty leather, and the fat-liquoring
must, therefore, be filling and softening. An emulsion of white curd
soap and olive oil, or of egg-yolk and neatsfoot oil, is suitable.
"Crestanol," a special preparation, also gives satisfactory results,
since it is adapted for giving nourishment and resiliency to thin,
empty leather.


FANCY LEATHERS

The best known of the fancy leathers is "morocco." This variety has
been made for ages, and the name probably originated from the fact
that very fine leathers of this kind were manufactured in Morocco a
few centuries ago. History records that a similar leather, dyed red,
was made in the ninth century before the Christian era.

The best morocco leather is made from Continental goat skins, which
are mostly obtained from Central Europe and Spain. The Norwegian goat
skins are also said to be of good quality for the morocco finish. An
inferior morocco leather, which is produced in large quantities, is
manufactured from East India goat skins, while a cheaper grade still
can be produced from certain classes of East India sheep skins. The
real moroccos are tanned in sumach, but the cheaper sorts are tanned
in India with babool or turwar bark and re-tanned in sumach in the
countries to which they are exported, chiefly Great Britain, Germany,
France, and America.

One of the best methods of sumach-tanning goat and calf skins is
that known as the "bottle" tannage. Each skin is doubled over and
sewn by machine round the edge, leaving part of the neck unsewn. The
skins are then turned inside out and filled with a strong infusion of
sumach, and floated in a tub containing sumach liquor. After being a
few hours in the tub, the skins are heaped one above the other in a
large pile, where the pressure forces the tannin through the skins.
The process can be completed in twenty to twenty-four hours, after
which the skins are cut open, rinsed, and finished in the usual
manner. This method of tanning is now largely replaced by the use of
paddle-vats (Fig. 25).

The dyeing and finishing are somewhat similar to that of coloured
boot upper leather, except that the leather is slightly oiled
on the grain instead of being fat-liquored. There are several
different methods of graining morocco leather; some of the grains
are made naturally by pressing the leather, when folded over, with a
cork-covered board, while others are first embossed in various ways
and then boarded. The well-known "crushed morocco" is produced by
glazing the grained leather under heavy pressure.

Skivers, the grain splits of sheep skins (see p. 145) are extensively
used for fancy articles. The majority are finished with a smooth
grain for hat-bands, bookbinding, and linings. The grain of a
sheep skin is, naturally, soft, and not very strong. To stiffen
and strengthen the grain, an artificial layer, consisting of paste
finishes, is often applied. Skins finished in this manner are termed
"paste grain skivers." These are largely used for bookbinding and
cheap purses. Sheep grains are sometimes given a finish somewhat
similar to that of leather bags. This is produced in a printing
machine by means of a copper roller which is run over the damp (but
not too wet) leather. The skins are then described as "long-grain"
skivers. The grain surface of sheep skins is particularly suitable
for embossing, and wonderful imitations of all kinds of skins can be
reproduced on skivers.

The fancy leather trade is not confined to these imitations, however,
as real lizard, seal, ichneumon, alligators, crocodile, shark,
porpoise, snake, and even frog skins (Japanese) are utilised.



INDEX


    Acid Swelling of Hides, 119

    Adulterated Leather, 114

    Ageing of Leather, 151

    Algarobilla, 43

    Alum Tannage, 150

    Annatto, 136

    Antelope Leather, 63

    Anthrax, 27, 69

    Arsenic Sulphide, 71


    Bablah, 45, 107

    Babool, 45, 107

    Band-knife Splitting Machine, 54

    Bark Mill, 93

    Barkometer, 97

    Bating, 86

    Belting Leather, 133

    Birch Bark, 106

    ---- Tar Oil, 107

    Bleaching Leather in Sun--_Frontispiece_

    Boot Leather, 137

    "Bottle" Tannage, 157

    Borax, 64

    "Box" Leather, 137

    Buffing Cylinder, 54

    Butts, 95

    Butyrate of Ammonia, 85, 129

    Butyric Acid, 85, 129


    Canaigre, 45

    Cape Sheep, 153

    Catechol Tannins, 46

    Caustic Soda, 66

    Celavina, 43

    Chamois Leather, 18, 144

    Chestnut Oak, 37

    ---- Tree, 36

    Chrome-quebracho Tan Liquor, 32

    Chrome Sole Leather, 125

    ---- Tanning, 108

    Cod Oil, 100, 120, 146

    Collodion, 136

    Colouring Pits, 94

    Combination Tannages, 111

    "Crestanol," 156

    "Crust" Leather, 151

    Currying, 133, 135

    Cutch, 46


    Dehairing Hides, 71

    ---- Knife, 80

    ---- Machine, 82

    Dehydration, 2

    Depilatories, 78, 149

    Disinfection of Hides, 2

    Divi-divi, 43

    Doling, 153

    Dressing Leathers, 102

    ---- of Leather, 112

    Drenching, 89

    "Dri-ped" Leather, 129

    Drum-tanned Leather, 103

    Drum Tumbler, 66

    Drying of Leather, 123

    Dust Colours, 154

    Dyeing, 112, 155

    Dye-wood Extracts, 139, 152, 155


    Ellagic Acid, 47, 121

    Enzymes, 72

    "Erodin," 88

    Evolution of Leather Manufacture, 1

    Extracts, 47


    Faller Stocks, 66, 146

    Fancy Leathers, 156

    Fat Liquors, 139

    Fellmongering, 145

    Finishing, 112, 122, 127

    Flaying: Mechanical method, 21

    ----: Pim's method, 24

    Fleshing Knife, 83

    ---- Machine, 82

    Fluffing, 128, 153

    ---- Machine, 129

    Foot and Mouth Disease, 6

    Formic Acid, 28, 66, 85, 95, 100

    Freezing Hides, 71

    Frizing, 145

    Fustic, 152


    Gallotannic Acid, 46

    Gambier, 40

    Glazed Kid, 137

    Glazing Machine, 143

    Gloving Leather, 147

    Goat Skins, 15

    Golden Tan Bark, 152

    Greasy Hides, 12

    ---- Sole Leather, 75


    Hammering Leather, 123

    Handlers, 94

    Harness Leather, 133

    Hauling and Setting Limes, 77

    Hemlock, 44

    Hide Markets, 7

    Hides and Skins, 5

    ----, Curing, 2, 26

    ----, Defects of, 19

    ----, Disinfection of, 2, 26

    ----, Horse, 17

    ----, Sources of Supply, 5

    Hyaline Layer, 68

    _Hypoderma bovis_, 30

    ---- _lineatum_, 30


    Japanese White Leather, 3


    Lactic Acid, 85, 95, 100, 129, 146

    Larch Bark, 45

    Layers, 94

    Leather-working Machinery, 52

    Liming, 71

    Linings, 145

    Logwood, 138

    "Lysol," 84


    Machinery, 52

    Mangrove, 41

    Marseilles Soap, 140

    Mimosa, 42

    Mineral Tannage, 108

    Mixed Tannages, 101

    Morocco Leather, 156

    Motor Leather Bands, 108

    Myrobalans, 38, 93


    "Neradol," 50


    Oak Bark, 34

    Oakwood, 35

    "Oropon," 87


    Paddle-vat, 146

    Parchment, 145

    Pickled Sheep Skins, 10

    Pigments, 154

    Pig Skins, 18, 136

    Pinning Leather, 121

    ---- Machine, 121

    Porpoise Laces, 19

    Preparation of Hides for Tanning, 63

    "Puerine," 88

    Puering, 150

    Pyrogallol Tannins, 46


    Quebracho, 32, 37


    Red Arsenic, 71, 149

    "Reeder" Splitting Machine, 145

    Roller Leather, 13

    Rolling Sole Leather, 122

    Rounding of Sole Leather, 95


    Saddlery Leather, 133

    Samming, 146

    Scudding, 86

    Seal Skins, 19

    Setting, 142

    Shaving Cylinder, 53

    ---- Knife, 55, 56

    ---- Machine, 56, 61

    Sheep Skins, 12

    Skins and Hides, 5

    Skivers, 145, 157

    Sleeker, 128

    Soaking Hides, 65

    Sod Oil, 147

    Sole Leather, 95

    "Soluble" Oils, 117

    Staking Machine, 143

    Sterilising Hides: Seymour-Jones's method, 28

    Straining, 128, 142

    Striking-out, 128, 130

    Stuffing, 135

    Suède Leather, 154

    Sulphide of Sodium, 66, 76

    Sulphonated Oils, 117

    Sumach, 38

    Suspender Pits, 94

    Synthetic Tannin, 49, 95


    Tanner's Beam, 68

    Tanning Extracts, 47, 92

    Tanning Materials, 32

    ---- Processes, 92

    Tan-yard, 94

    Tawing, 150

    _Terra japonica_, 40

    Tick Fever, 27

    Titanium Salts, 152

    "Tragasol," 117, 130, 140

    Turkey Red Oil, 141

    Turwar Bark, 156


    Vache Sole Leather, 132

    Valonia, 35


    Warble Fly, 28

    Wattle Bark, 42

    Weighted Leather, 114

    White Washable Leather, 155

    Willow Bark, 45, 106

    ---- Calf, 144

    Wool Skin Dressing, 51


THE END


_Printed by Sir Isaac Pitman & Sons, Ltd., Bath, England_





*** End of this LibraryBlog Digital Book "Leather - From the Raw Material to the Finished Product" ***

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