Leather: From the Raw Material to the Finished Product

K. J. Adcock

Leather: From the Raw Material to the Finished Product

Published by Good Press, 2022

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EAN 4057664561268

Table of Contents

CHAPTER I EVOLUTION OF THE ART OF LEATHER MANUFACTURE

CHAPTER II HIDES AND SKINS

CHAPTER III TANNING MATERIALS

Natural Tanning Materials

Tanning Extracts

Classification of Tanning Materials

Tanning Extracts

Synthetic Tannins

CHAPTER IV LEATHER WORKING MACHINERY

CHAPTER V PREPARATION OF HIDES AND SKINS FOR TANNING

CHAPTER VI TANNING PROCESSES

For Sole Leather.

For Dressing Leathers.

Mineral Tannages

Combination Tannages

CHAPTER VII THE DRESSING, DYEING, AND FINISHING OF LEATHER

Sole Leather

Chrome Sole Leather

Vache Sole Leather

Machine Belting, Harness, and Saddlery Leathers

Boot Upper Leathers

Chamois Leather

Gloving Leather

White Washable Leather

Fancy Leathers

INDEX

CHAPTER I

EVOLUTION OF THE ART OF LEATHER MANUFACTURE

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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

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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