The larger and heavier skins, such as those of buffaloes, bulls, oxen, horses and cows, are called “hides;” while those of the smaller animals, such as calves, sheep, pigs and goats, are called “skins.”
Scouring
The tanning of raw hides taken from animals is an ancient trade. The bark of trees made into a liquor has been used for centuries in treating practically all kinds of hides.
The oak, fir, hemlock and sumach are the most familiar of the many trees from which “tannin” is obtained for this purpose.
The cow hide is used practically altogether for sole leather and is bark tanned in the majority of cases. After the hide is taken from the animal it is either dry cured, or else salted green, and packed for shipment or storage.
The first process of preparing sole leather is to cut these hides in half or sides. The sides are then run through lime vats for the purpose of loosening the hair. They are then run through the unhairing machine, in which large rollers remove the hair.
From the unhairing machine the hides pass to a fleshing machine, which cuts away all the flesh or fat on the hide. They are then trimmed and scraped by hand, after which the real tanning process begins.
The old method of tanning leather was in large vats, which were filled alternately with tan bark and hides, then filled with water and allowed to soak for a period of eight to nine months before the tanning process was complete. The extract of bark in liquor form is used today by all large tanneries.