THE TANNER.

THE PITS.

Leather is a substance universally used amongst civilized and very generally amongst barbarous nations; it is made from the skins of animals, which are tanned, or prepared with some substance, having the power of converting the perishable skin, that decays readily when wet or moist, into a lasting and comparatively imperishable leather.

The preparation of skins by tanning or other similar processes has been practised from the earliest times; and although it has engaged the attention of several scientific men, and has been the subject of many curious experiments, it has received less alteration from recent improvements inchemical science than many other manufacturing processes. Several plans, which have been suggested with a view to expediting the process, which on the old system is a very tedious one, have been found to injure the quality of the leather, and have therefore been wholly or partially abandoned; and others, which appear to be more successful, are as yet adopted by a few manufacturers only.

The larger and heavier skins operated upon by the Tanner, as those of bulls, buffaloes, oxen, and cows, are technically distinguished ashides, while the nameskinsis 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 first be 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 decomposition. In the former case the horns are removed, and the hide is scraped to cleanse it from any small portions of flesh or fatty matter that may adhere to the inner skin; 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 rubbing 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 is loosened by a very slight 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 orbeam.

Unhairing the Hides. Striking the Hides.

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 a sour solution of rye or barley 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 “raising,” the pores of the hides are distended and rendered more susceptible of the action of the tan.

Oak-bark is the substance most commonly used to supply the astringent principle, and it is crushed or ground topowder in abark-mill. In the old method of tanning, which is not yet entirely abandoned, the hides and powdered bark were laid in alternate layers in thetan pit, which was then filled with water to the brim. After some months the pit was emptied, and refilled 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 improvement, introduced in consequence of the experiments of M. Seguin, a French chemist, of tanning with concentrated solutions of bark, formed by passing water through a mass of powdered bark, until, by successive filtrations, it is completely deprived of its soluble tanning principle.

Bark Box. Barrow.

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, of which considerable quantities are imported for the use of Tanners, produces leather of great solidity and weight, the colour of which is inclined to grey, and which is more impervious to water than that made with oak-bark. Valonia consists of the acorns of theQuercus Ægilops, and is brought from the Levant and the Morea. Catechu, or terra japonica, the extract of theAcacia Catechu, produces leather of a dark reddish fawn colour, which is light, spongy, and very pervious to water.

Fleshing Knife, and Section. Shaving Knife, and Section. Striking Pin, and Section. Unhairing Knife, and Section.

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.

We have hitherto alluded chiefly to the preparation of the thick hides used for sole leather, among which severalvarieties may be found, each distinguished by a different technical name, by which its thickness, quality, or mode of preparation is known; but the thinnest and weakest hides, as well as the skins of calves and other animals, are also prepared for use as upper leathers, in which case it is necessary to reduce their thickness byshavingorparingthem down upon the flesh or inner side, before they are subjected to the action of the tanning infusions. Such hides or skins also require, after leaving the hands of the Tanner, to be rubbed, softened, and dressed by the currier, in order to bring them to the necessary degree of flexibility and smoothness. The currier also has recourse to shaving or paring with a peculiarly formedknife, to bring the skin to the requisite tenuity; and it is his office to blacken the surface, which, for common shoe leather, is done on the flesh side, although for some purposes leather is blackened on the outer or grain side. Horse-hides, which are comparatively weak and thin, are sometimes dressed in the latter way, under the name of Cordovan hides, from the circumstance of such leather having been formerly made at Cordova, in Spain. Calf-skins supply the quality of leather most generally preferred for the upper part of boots and shoes.

Of the thin skins prepared for ornamental purposes, many are tanned with a substance calledsumach, prepared from a plant of the same name. The tanning is performed by sewing up each skin into the form of a bag, with the grain or hair side outwards, and nearly filling it with a strong solution ofsumachin water. The bag is then fully distended by blowing into it, and the aperture is tied up; after which it is thrown into a large shallow vessel filled with hot water containing a little sumach. The distendedbags float in this vessel, and are occasionally moved about with a wooden instrument until the solution which they contain has thoroughly penetrated their substance. Owing to the thinness of the skins and the heat to which they are exposed, this operation is performed in a few hours. The process is expedited by taking the bags out of the solution, and piling them upon a perforated bench or rack at the side of the tub, so that their own weight may force the confined liquid through the pores.

Apron. Gloves. Whetter. Roller. Leoline.

When the tanning is completed, the bags are opened to remove the sediment of the sumach; the skins are washed, rubbed on a board, and dried; after which they are ready for dyeing and finishing with a ridged instrument, which imparts to the surface that peculiar grain by which morocco leather is distinguished. An inferior kind of leather, known as “imitation morocco,” is prepared in a similar manner from sheepskins.

Plungers. Tongs. Jet. Hook.

“Tawing” is the name applied to the process by which the skins of lambs and kids are converted into soft leather bythe action of alum. Of this kind of leather gloves are usually made.

Thejetandplungersused for immersing the hides in the tan, thetongsandhookfor removing them, and the other implements, are easily understood as applied to the various processes here mentioned.

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