161 



LEATHER MANUFACTURE. 



LEATHER MANUFACTURE. 



163 



waistcoats, and other articles of dress are made. Mock or imitation 

 morocco, and most of the other coloured and dyed leathers used for 

 women's and children's shoes, carriage-linings, and the covering of 

 stools, chairs, sofas, writing-tables, Ike., are also made of sheepskin. 

 Lamb-skins are mostly dressed white or coloured for gloves ; and those 

 of goat' and kids supply the best qualities of light leather, the former 

 being the material of the best morocco, of all colours, while kid leather, 

 both white and coloured, affords the finest material for gloves and 

 ladies' shoes. Leather from goat-skins, ornamented and sometimes 

 gilt, was formerly used as a hanging or covering for walls. Deer and 

 antelope skins, shamoyed or dressed in oil, are used chiefly for riding- 

 breeches. Shamoyed leather breeches were formerly very much used, 

 especially in the army ; but being found unhealthy to horsemen 

 exposed to much wet weather, they were superseded by cloth trousers, 

 except in a few special regiments. Hone-hides, which, considering 

 their size, are thin, are tanned and curried, and are used by the harness- 

 maker, especially for collars ; and occasionally, when pared thin, for 

 the upper leathers of ladies' walking shoes. Dog-skins are thick and 

 tough, and make excellent leather ; but they have been in a great 

 measure superseded, as a material for dress shoes, by horse-leather and 

 by tanned rat-skins. Seal-skins produce a leather similar but inferior 

 to that supplied by dog-skins ; and hoy-skins afford a thin but dense 

 leather, which is used exclusively for covering the seats of saddles. 

 Porpoise-sking have lately been made, in Canada, into strong and 

 beautiful leather. 



Tanning. The larger and heavier skins operated upon by the tanner, 

 as those of bulls, buffaloes, oxen, and cows, are technically distin- 

 guished as hides ; while the name skins is applied to those of smaller 

 animals, as calves, sheep, and goats. The process necessary to convert 

 hides into the thick hard leather used for the soles of boots and shoes, 

 and for similar purposes, will be first noticed. The hides are brought 

 to the tanner either in a fresh state, when from animals recently 

 slaughtered, or, when imported from other countries, dried or salted, 

 and sometimes both, for the sake of preserving them from decomposi- 

 tion. In the former case the horns are remoced, and the hide is 

 scraped to cleanse'it from any small portions of flesh or fatty matter 

 which may adhere to the cutis ; but in the latter it is necessary to 

 soften the hides, and bring them as nearly as possible to the fresh 

 state, by steeping them in water, and repeated nibbing or beating. 

 After this the hair is removed ; sometimes by steeping the hides for 

 several days in a solution of lime and water, which has the effect of 

 loosening the hair and epidermis, or outer skin ; and sometimes by 

 suspending them in a close chamber called a smoke-house, heated a little 

 above the ordinary temperature of the atmosphere by means of a 

 smouldering fire ; in which case the epidermis becomes loosened by 

 incipient putrefaction. In either case, when the hair and epidermis, 

 or cuticle, are sufficiently loosened, they are removed by scraping with 

 a curved knife, the hide being laid upon a convex bench, or ' beam.' 

 The hides are prepared for the actual tanning, or immersion in a 

 solution of bark, by steeping them for a few days in a pit containing 



Fig. 1. Steeping Ilidei and Skin*. 



a sour solution of rye or tiarley flour, or in a very weak menstruum 

 consisting of one part of sulphuric acid mixed with from five hundred 

 to a thousand parts of water. By this process, which is called 

 ng,' the pores of the hides are distended and rendered more 

 susceptible of the action of {he tan, and the substance of the skin is 

 apparently increased ; but, as the process does not add to the gelatin of 

 the skin, a hide which is much thickened by the raising process loses 

 its subRtance when condensed by the shoemaker's hammer. 



Different tanners vary very much in the above processes. Some 

 believe that much of the original gelatin of the hides is never com- 

 bined with the tannin, but is wasted, owing to defective modes of 

 liming, unhairing, and cleansing. The German tanners often adopt a 

 process called iterating, by laying the hides in a pack or pile, and 



ARTS AND SCI. DIV. VOL. V. 



covering them with speut tan to produce a fermentative heat. On 

 these points much remains yet to be discovered. There are also many 

 variations in practice, in relation to the actual tanning, or conversion 

 of the prepared pelt into leather. Oak bark, crushed or ground to a 

 coarse powder in a bark-mill, is the substance most commonly used 

 to supply the astringent principle. In the old method of tanning, 

 which is not yet entirely abandoned, the hides and powdered bark 

 were laid in alternate layers in the tan-pit, which was then filled with 

 water to the brim. After some months the pit was emptied and 

 re-filled with fresh bark and water ; and this process was repeated 

 whenever the strength of the bark was exhausted. In this way the 

 time required for impregnating the hides varied, according to their 

 thickness and other circumstances, from one to four years. The 

 process has been greatly expedited by the improvements introduced in 

 consequence of the experiments of M. Seguin, a French chemist; 

 nevertheless it may be well to observe that skins which are quickly 

 tanned, by the use of strong solutions, produce leather of less durable 

 quality than that which is slowly formed: 100 Ibs. of skin, quickly 

 tanned in a strong solution of bark, will produce 137 Ibs of leather, 

 while the same weight of skin, slowly tanned in a weak solution, 

 produces only 117 Ibs.; the additional 1941bs. in the former case 

 tending to swell the tanner's bill, although it deteriorates the leather, 

 and causes it to contain less of the animal solid. 



The variations of practice among different tanners extend to the 

 substance used as an astringent, as well as to the manner of applying 

 it. Ground oak -bark, which was formerly the only material in common 

 use, and is still the most general, produces good leather of a light fawn 

 colour. Valonia produces leather of great solidity and weight, the 

 colour of which is inclined to gray, and which is more impervious to 

 water than that made with oak-bark. Catechu, or terra-japonica, pro- 

 duces leather of a dark reddish fawn colour, which is light, spongy, and 

 very pervious to water. Another substance which has been used of late 

 years is a kind of bean-pod, called divi-divi. These substances may be 

 used either individually or in various combinations. In the methods of 

 preparing tanning solutions there is also considerable variety. Some 

 tanners use cold water for the purpose, and others hot water or steam ; 

 others again, instead of pure water, employ ooze, or tanning liquid which 

 has been exhausted by use. A further point of difference is found in the 

 strength of the solutions used, which vary exceedingly. When the im- 

 pregnation of the hides with tannin is effected by laying them flat in the 

 tan-pits, they are frequently taken out to renew the solution ; and the 

 skins which have lain near the top of one-pit are laid near the bottom 

 of the next, so as to equalise the amount of hydrostatic pressure. Some- 

 times the tanning is facilitated by suspending the skins vertically in 

 the liquid, by which means they are penetrated quickly ; but the plan 

 requires considerable room, and, unless the skins are frequently moved, 

 it occasions injurious folds in the leather. Another plan, which 

 answers well for small light skins that require but a short time for 

 tanning, is to sew up each skin into the form of a bag, to fill it with 

 tau-liquor, and then immerse it in the pit. The great space required 

 is the principal objection to this plan. In whichever of the above ways 

 the tanning is effected, the hide is subjected to the action of solutions 

 increasing progressively in strength, until it is so perfectly penetrated, 

 that when cut through it presents a uniform brown colour ; any 

 appearance of a light streak in the middle of its thickness being an 

 indication of imperfect tanning. When the process is complete, the 

 hides are hung up in a shed, and allowed to dry slowly ; and, while 

 they are drying, they are compressed by beating or rubbing, or by 

 passing them between rollers, to give them firmness and density. A 

 yellow deposit is now found upon the surface of the leather, to which 

 the name of bloom or pitching is technically given; and, although 

 this deposit is subsequently removed by the shoemaker in the operation 

 of buffing, and forms a useless addition to the weight and cost of the 

 leather, the prejudice of purchasers requires that it be left on the 

 surface by the tanner. 



Although, owing to the many differences in the practice of tanning, 

 no definite time can be stated for the various operations mentioned 

 above, it may be observed that the \isual period required for tanning 

 such hides as are used for the soles of men's boots is from six to 

 twelve months ; and that from fifteen to eighteen months are required 

 in preparing those of the thickest kinds, which are termed butts or 

 backs. Occasionally hippopotamus hides are tanned, requiring an 

 enormous time for the process; and instances have been known of wild 

 boar hides remaining seven years in tan, to produce leather two inches 

 in thickness. 



Before describing the processes for thinner leather, it will be neces- 

 sary briefly to notice some among the numerous plans for shortening 

 the time involved in the tanning of thick hides. Several schemes have 

 been devised for forcing a tanning solution through the pores of the 

 hide by mechanical pressure. Mr. Spilsbury obtained a patent for this 

 purpose some years ago ; but it failed ; for it appears that tannate of 

 gelatin was formed on the outer sides of the skins in the form of long 

 masses of slime ; while the leather had lost much in weight, was very 

 porous, and unequally tanned, in consequence of the tan-liquor pene- 

 trating most readily the thinnest or weakest parts of the hide. A 

 process patented by Mr. Drake consisted in sewing two skins together 

 (after they had received a slight tanning in the ordinary way), so us to 

 form a water-tight bag, which was tilled with tan-liquor. The bag thus 



M 



