Liming and unhairing, which swell the hides and dissolve the perishable animal portion, loosen the hair, and put the hides into proper condition for tanning. Hides tanned without liming, even if the hair is removed by some chemical, do not make pliable leather, but are stiff and hard.
Bating, which removes the lime from the hides.
Pickling, which helps in the tanning later, and keeps the hides and skins from spoiling if they are not tanned at once.
The lumps of fat and flesh that may be on the hides are removed by machinery or by placing the hide over a beam and scraping it with a knife. The hair, when it is loosened by the lime, is removed by a machine or by hand.
CHAPTER THREE
PROCESSES OF TANNING
The various processes of tanning may be roughly divided into two classes, vegetable chemical and mineral chemical. The first class is often spoken of in tanneries simply as the “vegetable” while the second is called “chemical” process. In the vegetable processes the tanning is accomplished by tannin, which is found in various barks and woods of trees and leaves of plants. In the so-called chemical processes the tanning is done with mineral salts and acids which produce an entirely different kind of leather from that procured by vegetable tanning.
There is also a method of tanning, or, more properly speaking, tawing, in which alum and salt are used. This process makes white leather that is used for many purposes; it is also colored and used in the manufacture of fine gloves. Leather is also made by tanning skins with oil. Chamois skins are made in this way.
The materials that are used to tan hides and skins act upon the hide fibers in such a way that the hides are rendered proof against decay and become pliable and strong. There are many vegetable tans; they are used for sole leather, upper leather, and colored leather for numerous purposes. The bark of hemlock trees is one of the principal tans. The woods and barks of oak, chestnut, and quebracho trees are often used. Palmetto roots yield a good tan. Large quantities of leather are treated with gambier and various other tanning materials that come from foreign countries. Sumac leaves, which are imported from Sicily, contain tannin that makes soft leather suitable for hat sweatbands, suspender trimmings, etc. Sumac is also obtained from the State of Virginia, but the foreign leaves contain more tannin and make better leather than the American.