The art of tanning leather ..

Front matter

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Class Book.

SMITHSONIAN DEPOSIT

Chapter II

The different kinds of Skins suitable for Tanning— Buenos Ayres hides — Brazilian hides — Cow-hides — American Ox-hides — Spanish or South American dry hides — Calcutta or Nagore hides — Calf-skins — Horse-hides — Goat-skins — Sheep-skins — Deer-skins — and the Mode of Salting hides 37

6 CONTENTS.

Page.

Preface

The following directions have been prepared expressly for information as to the practical application of scientific principles which characterize the progress of the improvement, and are offered to that portion of the public which is interested in the leather and tanning business.

Like every other art, that of tanning has lately made great progress towards perfection. Ingenious and practical men have devoted their energies to actual experiments, and chemical agencies have been employed with varied success,

12 PREFACE.

until, at length, the desideratum seems to have been attained, which affords a new and complete substitute for -the manufacturing of all kinds of leather. This must soon give it a world-wide celebrity, and entitle it to the attention of all concerned in the leather business. The Patentee, Mr. K., takes great pleasure in giving a comprehensive description of the different preparations for using the improvement ; and I subscribe my hearty good wishes for the success of the invention for the purpose of procuring the desired information. Inquiries have been directed to the consultation of Sir Humphrey Davy, Professors Turner and Ure, and several other celebrated authors. In this way the author has obtained the most accurate knowledge of the chemistry of tanning, and for giving a full and comprehensive treatise on changing hides into leather.

Chapter I. Introduction

The art of tanning is that by which animal skins are converted into leather, a product differing entirely from that of the raw material, and adapting it to the useful purpose for which it is employed. The properties imparted are of a physical nature, and vary with the kind of skin employed and the modifications of the process which it undergoes. Chemically considered, however, leather is a definite compound of tannin and gelatin. Tanning, as an art, dates as far back as nine hundred years before Christ. The methods resorted to in early times consisted of little more than merely cleansing and drying the skins ; and, thus prepared, the latter were used for clothing, &c. Leather was largely in use among the ancient Egyptians, and the workers of that material were so numerous that the Memnonian quarter, Thebes, was characterized as their especial locality. Their skill in fashioning it was so great that ornaments of all shapes and devices were made from it. Leather was made by them into tapestry, and many of the Egyptian tombs bear representations of artificers in leather engaged in the several branches of their vocation.

The principal steps in the manufacture of leather are the washing and soaking, for the purpose of cleaning and softening the skins, and preparing them for the removal of the hair. This is effected by the use of lime, or other substances which destroy, dissolve, or soften the bulbous roots of the hair, and thus facilitate its removal by mere mechanical scraping with a bluntedged knife. During this part of the process, another important end is generally accomplished in the swelling of the tissues and their preparations for the more complete and easy absorption of the tanning principle. The primitive mode of removing the hair was that of shaving it off with a knife ; but the use of lime was known even among the early Egyptians. When the rationale of depilation is better understood by practical tanners, the slow and inconvenient process of depilation by means of lime must give place to more effective, rapid, and economical methods. In later times, these defects were remedied by immersing the cleansed and dehaired skin in an infusion of oak bark or solution of alum, and thus, by effecting a union between one or more constituents of the liquor and a gelatinous tissue of the skin, producing a newcompound with desirable properties. The principles governing this reaction have been, in more recent days, developed by the investigations of Proust, Deyeaux, McBride, and Sir Humphrey Davy ; and it is owing to the researches of these inquirers that the occupation of the tanner has been elevated from the condition of an empirical pursuit to that of an art based upon scientific principles. Many improvements in the art have been made by the aid of ingeniously contrived machinery, and much has been done to hasten the process of tanning.

Tanning consists in the combination of the gelatinous tissue with tannin by immersing the skins in an infusion of oak bark or other substances containing tannin. The tanning influence is probably not exerted solely by the tannin, but also partly by the extractive matter, more or less of which always exists in the tanning material.

During the soaking, the epidermis of the skins disappears, and the tissue of the latter is gelatinized, and thus predisposed to chemical union with the tannin. This gelatinization of the tissues is allessential, and is promoted by the gallic acid fermentation of the tanning material. This is the more probable science. The same effect may be produced by the use of a very dilute acetic, and other operations intended to perfect the quality and appearance of the leather. Leather is employed for many useful and ornamental purposes ; and numerous

2* are its applications to various branches of industry. Besides its extensive use for covering the head and feet, wearing apparel, saddles, harness, carriages, and the purposes of the book-binder, it is largely employed for the embellishment of objects of taste and ornament. Independently of the direct importance of the leather trade, it exerts a very decided incidental influence in developing the resources of a country, by giving value to certain materials used in and resulting from its manufacture. Besides the immense employment which it gives to thousands of artisans, it has built up colonies and towns, which owe their origin and progress entirely to the interests connected with it. Even the waste materials of slaughter-houses, tanneries, curriers' shops and workers in leather, have important applications — the horns serving for the manufacture of combs, buttons, and umbrella furniture ; the hair for plastering ; the spent lime for the farmer; the skin-clippings for the glue-boiler ; and the leather shavings for the manufacturer of prussiate of potash. The following statements will give an idea of the vast extent and rapid increase of the trade in leather.

In France — a country eminent for the quantity and quality of the leather which it produces — the average number of skins annually converted into leather is about three millions of whole skins, exclusive of sheep and calf skins. In the United States, the manufacture of leather is only beginning to be of much importance. Since the early part of the present century it has been rapidly extended, until it has become, with its allied and dependent arts, one of the most prominent elements of national prosperity. This improved system is conducted in the most simple and primitive manner. The expenditure both of time and labor is now materially reduced by the different modes and treatment of the process. The unparalleled success which has attended the introduction of the patent process set forth in this work, and the nattering encomiums bestowed upon the directions given in a former edition, induce me to extend them a little farther, hoping they will be understood by all those who will avail themselves of this improved system for the manufacture of leather.

I have extended the information in this, the third edition of directions, and hope that my fellow-tanners will read them with a generous allowance for the imperfect style in which they are given ; hoping, also, that they will keep in mind that they are not fiction, but sober truths, intended expressly for the application of the process.

For some time past my whole time and attention have been given exclusively to the introduction of this process, believing from the first that its merits would, in time, bring it into general use, which is now acknowledged to be a fixed fact by those most conversant with it. Its general adoption is now only a question of time ; for as fast as it becomes known it is adopted. This being the case, I wish to give all the information I can respecting the manner and different methods of using it. To those tanners who have adopted and seen fit to recommend this new process for tanning leather, I return my sincere thanks, and assure them that their kindness to me, and approbation of the improvement, wi]l not be forgotten.

We append a statistical table, compiled from the returns of the seventh census, showing the condition of the tanning interest.

The National Intelligencer compiles, from the census returns, the following table of the tanneries in the United States, in A. D. 1850 :

No. of establishments, . . 9,263

Capital invested, . . . $18,900,557

Value of raw material, . 19,613,237

Value of product, . . . 32,861,796

The number of hides is 6,128,070; skins, 2,653,865; and about 6,000,000 sheep, goat, and other small skins tanned and dressed annually, which are not included in the number. The number of hands employed is 20,909 males and 102 females. The monthly wages of the males amount to $416,214 ; of the females, $970. The number of sides of leather produced annually, is 12,557,940, and of skins, 27653,865.

The foregoing estimates were carefully compiled from the returns of the seventh census, for the National Intelligencer, and may be considered correct.

Leather forms one of the heaviest items among the staples of American merchandise, and the demands for it are daily increasing, in addition to its extensive employment for the embellishment of objects of taste and ornament.

If we take it for granted that the leather trade has advanced in amount at the rate of 10 per cent, per annum, for the last seven years, the figures should now stand thus :

Amount of capital invested, .... $32,030,946 90 Value of raw material, 33,342,502 90 Value of product, . . 55,865,053 20

These calculations may fall short of, but it is believed that they do not exceed, the truth. They may at least serve to indicate the vast extent and rapid increase of the leather trade in this country. But what must it be a quarter of a century hence \

At the present rate of increase, we may fairly calculate that in twenty-five years hence the tanning and currying business will have teipled, thus placing it almost in the van of all domestic manufactures. A business of such extent and importance, well deserves the attention of the manufacturer, for whatever abridges and facilitates the process, adds to the value of the capital invested.

The claims of this Patent are reasonable and philosophical. Tanning is wholly a chemical process, converting hides into leather. The perfection of the results of this process, depends not so much upon the energy and proper combination of such astringent properties and chemicals as are employed to effect it. The more rapid the action of these agents, and the quicker their work is done, the more perfect is the article manufactured. This is the doctrine of the improvement set forth in this work ; and its correctness, economy, and great utility, we are ready to submit to the scrutiny of science and the test of the most thorough experiment.

The leather manufactured by this process is of a finer texture, softer, susceptible of a higher finish, less porous, more pliable, stronger, heavier, and more durable than leather tanned in the ordinary way. The quality of the material itself — which any man may examine — and its use and trial for years, authorize these high claims. They are announced to the public with the most implicit confidence in their accuracy and reliability.

We respectfully invite particular attention to the following statements : — ■

The numerous and great advantages of this improvement, both to the manufacturer and to the consumer, are matters on which the most satisfactory information may be obtained.

The adoption of this process by every tanner in the United States is practicable. It consists chiefly in the application of a proper compound or combination of certain chemicals to the usual bark, liquors or other astringent properties, possessing tannin, thereby causing a much more rapid advancement in the tanning of leather than is or can be produced by the ordinary process. It requires no new fixtures or expensive outlay. After the hides are tanned by this process, the scouring, stuffing, oiling, blackening, and finishing are conducted as they ever have been.

This improvement will be found of great general economy and utility. A correct knowledge of it must secure its universal adoption. The following facts sustain this conclusion:- — Many of the most experienced, scientific, and enlightened tanners and other artisans connected with the manufacture or sale of leather, have certified to the superior excellence of the leather manufactured by this process, as possessing all the essential properties requisite for beauty and utility. We believe a similar opinion is entertained by all who have carefully examined the leather, and who are competent to form a correct judgment of the article manufactured.

To capitalists, and especially to those who have invested large amounts of money in the manufacture of leather, the following estimates, showing the difference in the expense of tanning, between the old method and this patent process of tanning, will be interesting : —

ONE YEAE'S WOKK BY THE OLD METHOD.

To present this matter so as it may be readily comprehended by those doing a small business, we will exhibit it on a a small scale. Under the old metiiod of tanning with bark, two men will tan and finish 4,000 sides of sole leather in one year. Their wages, at $30 per month, will be $720 ; the sides, in the raw and dry state, will weigh on an average, 11 lbs. per side, making 44,000 lbs. ; at 32 cents per lb., they will cost $14,080 ; they will consume 270 cords of oak bark, at $7 per cord, making $1,890 ; rent of tan-yard, $150, interest on hides, $844 80; interest on bark,

$113 40; whole cost when finished, is $17,798 20. The 4,000 sides of leather will weigh on an average, 16 lbs. per side, making 64,000 lbs. At 32 cents per lb. they would bring $20,480, affording a net gain of $2,681 80 for one year's tanning on the old system.

one year's work by this new

PROCESS.

Under this patented improved system of tanning, one man will tan and finish 4,000 sides in one year. At $30 per month, his wages will be $360 ; the sides will weigh on an average in the raw and dry state, 11 lbs. per side, making 44,000 lbs.; at 32 cents per lb. they will cost $14,080 ; they will consume 135 cords of bark at $7 per cord, making $945, and chemicals to the amount of $600; rent of tan-yard, $150; the interest on the hides for six months, will be $422 40 ; the interest on the chemicals will be $18 ; the interest on the bark will be $28 35 ; making the whole cost of tanning 4,000 sides under this system, only $16,243 75. The weight of the 4,000 sides when finished, will be, on an average, 17 lbs. per side, making 68,000 lbs. of leather — a gain in weight of 4,000 lbs. over those tanned by the old method at 32 cents per lb. ; —the whole would bring $21,760. The net gain is $5,516 25. Showing an advantage over the old method of tanning in one year, even on this limited scale, of $2,834 45 ; besides, the leather tanned by this process has a brighter color, more the appearance of oak-tanned leather, and commands a higher price in the market.

The above is a clear and accurate calculation of the cost of tanning, both with this process and the old method, and the result makes its own appeal to the good sense of all who are anywise interested in the profits arising from leather. Tanners ! see yon not that if so much can be saved by applying this patent process to tanning on so diminutive a scale, that the ratio of profit would be vastly increased by employing it on a more extended plan ? You are invited to investigate this matter. If, on examination, you find that a substantial saving of even ten or fifteen per cent, can be made on a year's business by adopting this new process, you will not fail to see where your interest leads you ; for ten per cent, over and above your accustomed profits would, in a few years, secure for you an independent fortune.

It is plain that the advantages of this mode of tanning, even to one who tans only sole leather on a small scale, are very great ; and to those who find it difficult to obtain the usual quantity of bark, it will be invaluable. Where bark is plenty and can be obtained at a small cost, it also is valuable, for only one-half the usual quantity of bark will be found necessary. By adopting this method then, the tanner who consumes 1,000 cords of bark per year, will require only 500 cords ; a saving at once of from $1,600 to $2,000 on bark alone, in one year.

A brief summary of the advantages of this patent process of tanning, may be stated thus :

Hides or skins can be tanned at much less expense than by the usual method. Common size calf, sheep, goat, deer, or other similar skins, can be tanned in from four to twelve days, at an expense of from fifty cents to one dollar and fifty cents per dozen. Heavier leather,

INTRODUCTION.

such as kip, upper, bridle, skirting, harness, and sole leather, can be tanned in from twenty to ninety days, with a proportionate increase of expense, according to the thickness of the hide and strength of liquors used.

The liquors used in this process are in all cases applied to the hides or skins only in a cold state, and the leather manufactured by it has been found to possess more pliability, greater strength and durability, and a much larger increase of weight. It forms a finer texture, and gives it a handsomer bloom, and consequently finishes much better ; thereby rendering it more impervious to water than leather tanned by the old method.

The whole process can be learned by any tanner in a very short time.

The apparatus and the different stages of the process of tanning, are the same or similar to the usual method ; but capable, in fitting a new establishment, of being more compactly arranged, and at much less expense.

It requires less room or space to carry on the business.

Parties wishing to satisfy themselves on any point named in this or any other chapter of this work on which it is proper to give general information, are invited to call on the patentee or his agent, and examine the system in its practical operations, see the leather manufactured, and witness experiments which they are prepared to make at any time, for the purpose of illustrating and corroborating the claims of this patent, for which letters were granted on the 14th day of April, 1857.

Chapter II. The Hides Suitable For Tanning

The hides and skins retain their original name nntil they have been subjected to the treatment of the various processes they have to undergo before they become leather. The quality of leather depends not only upon the nature of the skin and the mode of tanning it, but upon the result of numerous minor details, which require especial care and attention. Skins from large cattle are best, provided they are not thin and flabby, for such will make only inferior leather. Those from cattle slaughtered in the colder months give five per cent, more leather than hides taken in summer. The nature of the food and state of the animal's health, also, 'have an influence upon the quality of the hide. For the production of forty pounds of leather, there are required, on an average, twenty-five pounds of dry hide, fifty-six pounds of salted hide, or seventy pounds of marked hide.

SPANISH, OR WILD BULLOCK.

Buenos Ayres hides are taken from the wild cattle which are run down by hunters. After being removed from the carcass they are spread upon the ground, with the flesh side uppermost, and left exposed to the sun and air until dry. To prevent shrinking, the hides are kept stretched by means of wooden pegs driven through the corners into the earth.

One of these cattle, a Spanish bullock of the largest size, is before represented ; and also the natives or hunters in search of wild cattle are represented by a wood engraving in front of this chapter.

Brazilian hides are nearly all slaughtered in the ordinary manner. It would be greatly to the interest of the tanner, and would save him much annoyance, if all hides were imported in a green state : that is, merely salted ; for, when dry, it is very difficult even for the most experienced to detect many defects which would impair the quality of the leather into which they are to be converted. The large ox hides are the ones chiefly used for conversion into sole leather; for cow skins, though of denser structure, are rather too thin for this purpose, and are, therefore, reserved for making saddler's leather. This remark applies only to the hides of old cows that have repeatedly calved.

OLD COW.

These are weak and distended, but often tan well, and make good harness leather, and sometimes make a very good quality of upper leather. The hides of heifers, on the contrary, are equal, if not superior, to those of oxen.

Bull hides, on the other hand, are the least esteemed for making good leather, being thinner and more flabby than those of either oxen or cows.

AMERICAN FAT WORKING OX.

A well-fed, moderately-worked ox, when slaughtered in a healthy condition, will naturally yield a hide of normal quality; but if sick, lean, or deficient in hair at the time of being killed, then the hide is not adapted for making good leather. Should the animal die suddenly by accident, without being in a diseased condition, the quality of the hide is not thereby impaired. The hides from unhealthy bullocks or horses present a decided difference from those of the same animals slaughtered in a sound condition. This difference is not distinguishable by any very evident characteristic, though it seldom escapes the sagacity of an experienced tanner. There are no definite rules for estimating the quality of hides. If a skin is free from any defects, and has sufficient strength and thickness, with body and firmness, then it may be presumed that it will tan well and make good leather.

A skin presenting the opposite characteristics— that is, flabby, soft, thin, weak, and will not bear handling — should not be considered reliable. These signs, however, are not always unerring, for anomalous cases frequently occur. Indeed.

FOR TANNING.

it may sometimes happen that the hides from a diseased carcass, differing in appearance from the rest, will produce excellent leather.

As the skins could not be kept any length of time in a fresh state without being injured by putrefaction ; and as it would be impossible to transfer them as soon as slaughtered to the tan vats, they are preserved unaltered by salting or drying them. The country butchers stretch them out in drying-lofts or in the shade, while those in the city generally salt them. In the sale of unsalted green hides there are certain reprehensible frauds which it is difficult to provide against. For instance^ not only are the horns, ears, and other less valuable parts left upon the skin, but some butchers, in order still further to increase its weight, beds the animal before slaughtering in filth and mire, and then, after skinning it, trail the hide on the dusty ground.

Domestic, slaughtered, and heavy hides are converted into sole, belt, and harness leather. The very largest are selected and enameled for carriage tops. The smaller and lighter ones are used for skirting and bridle leather. In the old method they have to undergo a bleaching process, termed fair finish, which is avoided in this process of tanning. The smaller hides are sometimes converted into upper, and also for enameling and japanning, termed patent leather, when intended for shoes. The hides from the northern latitudes are preferable to those from the south. Hides from the extreme south are particularly objectionable for conversion into leather. Those from California, when free from the defects caused by unskillful skinning, are of good quality.

and will tan well and make good leather.

SPANISH BULLOCK.

Spanish or South American dry hides are generally converted into sole leather and occasionally into "belt leather. Those imported in the green and salted state are sometimes made into upper leather, which is of fair quality.

African hides from the west coast make good uppers ; but they are largely used in their raw state for covering hair trunks. Madagascar hides are good when perfect, which is rarely the case, as they are liable to injury during curing transit.

The hides of the neat yearlings go into calf skins. Of these latter, there are "patna" kips, and common calf for bookbinders. The patna' kips are very inferior, though frequently sold as " Calcutta kips."

CALCUTTA, OR NAGORE BULLOCK.

Calcutta or Nag ore Cattle. — These cattle grow to a very large size, and are used in India by the higher orders to draw their state carriages, and are much valued for their size, speed, and endurance, and sell at very high prices. They will travel, with a rider on their back, fifteen or sixteen hours a day, at the rate of six miles an hour. Their action is particularly fine. The Nagore cattle bring their hind legs under them in as straight a line as the horse. They are very active, and can clear a five-barred gate with the greatest ease.

Hides from Calcutta or Nagore cattle have the distinctive property of greater weight, and, when perfectly tanned, make a superior quality of leather. Tanners have undertaken to tan them, but failed in the experiment and pronounced the hides worthless.

I, at one time, for an experiment, tanned six dozen of Calcutta kip skins, in the space of fourteen days, by this process of tanning ; and the leather produced was of a very handsome quality. They were pronounced to be a superior article of leather by some of the best judges and most experienced leather manufacturers. One dozen of those skins were taken to the State fair in Pennsylvania, and were awarded the first premium for being the best leather on exhibition. These kips sold at an advance price of fifteen per cent, in the Philadelphia market.

Hides from the largest of these cattle are best suited for making good leather, being strong and heavy, provided they have not undergone any injury during the importation.

A few kips come from South America, and some from England and Ireland. The supplies of the tanneries are mostly domestic skins.

CALF READY FOR SLAUGHTERING.

Calf Skins are valued in proportion to their strength and size, and, when properly tanned, make excellent leather for boots and shoes, and also make superior patent japanned (termed patent calf skin) leather for fine wear. The skins of young calves are sometimes converted into parchment. The French tanners, who are renowned for the excellence of their calf leather, use the skins taken from animals of Hve or six months of age. Those from calves of less than two months old are very inferior, and only suitable for the manufacture of parchment.

Calf skins tanned by this process have superior advantages over those tanned by the old method. I have frequently heard gentlemen say they wore a pair of calf-skin boots on their feet which were manufactured from leather tanned by this process, and that they have worn them every day for a period of four months, without overshoes, and their feet have not been damp once, though they have repeatedly walked in the snow and sleet; and at present there is not the slightest appearance of cracking in the uppers, and the soles are apparently as good as the first day they put them on their feet. Calf-skins tanned by this process possess more strength, have a finer texture, and produce a handsomer grain ; are more pliable and durable, and more impervious to moisture, than when tanned by the old method.

MUSTANG, OR WILD HORSE.

Hoese Hides are tanned for uppers, and make good leather. They are also tanned for thongs, for sewing belts, &c, and are the best material for that purpose. Horse hides make good leather for japanning and enameling purposes ; when well tanned and properly finished, make a superior leather for shoes and fancy mountings for ornaments of taste.

Goat Skins, when tanned and curried, are used for the uppers of ladies' shoes. Tanned in a particular manner and dyed with fancy colors, they constitute

Morocco or Turkey leather. The best goat skins come from Mexico, and are known in commerce as Tampico skins. The sound skins from the Cape of Good Hope are very large, and far superior to those from Madras and the Cape de Verds. Goat skins, when properly tanned and manufactured into good Morocco, make a superior leather for ladies' and gentlemen's wear, which is soft and pliable to the feet.

SHEEP AND LAMB.