This branch of leather manufacture is mainly carried on in Germany, Austria, and France. In Germany and Austria, lamb-skins are principally employed; in France, kid-skins. For fine gloves, the skins of very young animals only can be used. The commonest style of manufacture is as follows: - The soaking of the dried skins is effected in large wooden tubs, and occupies on the average 3 or 4 days, according to the. character of the soak-water, the size of the skins, and the time they have been stored. The skins, when thoroughly and uniformly softened, are unhaired either by painting the flesh side with a thin paste of lime, or in lime-pits. In unhairing by painting, the skins, after coating the flesh side with lime, are folded together, so that the lime comes as little as possible into contact with the wool, and these bundles or " cushions " are placed in a tub, in which they are most frequently covered with water. After unhairing on the beam with a blunt knife, the skins must be limed for some days, in order that the leather may stretch well, a quality which the Germans denominate Zug. By this method of unhairing, the wool is preserved uninjured, but it is not suitable for the finer sorts of leather.
The unhairing in lime-pits is done either with gas-lime, or, as is now almost exclusively the practice, with the so-called " poison-lime." This is prepared by mixing red arsenic (arsenic sulphide) with lime, while it is being slaked, and is at its hottest. The calcic sulphydrate (and perhaps sulpharsenite) thus formed hastens the unhairing, and gives the grain a higher gloss. Well-conducted establishments now avoid as much as possible the use of old limes, which produce a loose, porous leather, with a rough, dull grain. The liming lasts on the average 10 days, and is of the greatest importance. It is essential that the interfibrillary substance shall be dissolved, that the leather, may have the quality known as Stand, that is to say, may be strongly stretched in either length or breadth without springing back. It also depends upon the liming (and this is of special importance in the case of lamb-skins) whether the tissue of the fat-glands is well loosened, so that the fat, either as such, or as lime-or ammonia-soap, may be readily and completely worked out.
Skins in which this is neglected can never be properly dyed.
When the hair (or wool) is well loosened, the skins are rinsed in water, and then unhaired on the beam with a blunt knife. The water employed in washing should not be much colder than the limes, or it will prevent the hair from coming away readily. The wool or hair is washed and dried for sale. The skins are thrown into water to which a little lime-liquor has been added, to prevenl precipitation of the lime in the skins by the free carbonic acid of the water, which would have the effect of making them rough-grained.
Next comes the first fleshing or "levelling." By this, the loose cellular tissue on the flesh side is removed, together with the head, ears, and shanks, and the flanks are trimmed. The skins are then again thrown into water, softened with lime-liquor as above described, and then into a bate of dogs' dung. This is prepared by stirring up white and putrid dogs' dung with boiling water, and straining it through a sieve or wicker basket. The bate must be used tepid, and not too strong. The skins " fall (lose their plumpness) in it rapidly, and become extremely soft and fine to the touch; and the fat-glands, remaining hairs, and other dirt, can now be very readily scudded out. So far, no completely satisfactory substitute has been found for this somewhat disgusting mixture, but it has been noted that guano will produce similar effects. With regard to the mode of action of the dung-bate, much has been speculated without proof, and exact analytical evidence is wanting; but no doubt a weak putrefactive action goes on, as may be deduced from the presence of bacteria; further, the ammonia and weak organic acids present in the putrefying dung are capable of acting on fat and lime; and finally, a direct mechanical effect seems to be produced, difficult to describe, but favourable to the succeeding manipulation.
Too strong bates, or too long continuance in them, produces evident putrefactive effects on the skins.
When the skins come out of the bate, they are stretched and worked on the flesh with a sharp knife, and any remaining subcutaneous tissue is removed. This constitutes the second fleshing. They are then rinsed in warm water, and beaten with clubs in a tub, or worked in a tumbler drum, in either case with a very little water only; and finally brought into a tank of water, not too cold, and kept in constant motion with a paddle-wheel.
The skins are next cleansed on the grain-side by working on the beam with plates of vulcanite with wooden handles, so as to remove fat, lime, and ammonia soaps, and other lime compounds, together with all remaining hair or wool. The skins are now a second time washed in the "paddle-tumbler," first in cold and then in tepid water; and after allowing the water to drain from them, they are transferred to the bran-drench.