Butts and backs are selected from the stoutest and heaviest oxhides. The butt is formed by cutting off the head, the shoulder, and the strip of the belly. The butt or back of oxhide forms the stoutest and heaviest leather, such as is used for soles of boots, harness, etc.
Green-Salted Calfskin. [Page 12.]
Hides and skins are received at the tannery in one of three conditions, viz. green-salted, dry, or dry-salted. Very few hides are received by tanners in fresh or unsalted condition, salt being necessary to preserve them from decay. Green-salted hides are those that have been salted in fresh condition, tied up in bundles, and shipped to the tanner. Dry hides are those that were taken from the carcass and dried without being salted; these are usually stiff and hard. Dry-salted hides are hides that were heavily salted while they were fresh, and then dried. The hides and skins that are received from the slaughterhouses of this country are almost invariably green-salted; those from foreign countries are green-salted, dry, and dry-salted.
It does not matter in what condition the hides are received or the kind of leather into which they are to be tanned; they all require soaking in water before any attempt is made to remove the hair or to tan them. The object of the soaking process, as it is called, is to thoroughly soften the hides and to remove from them all salt, dirt, blood, etc. Ordinary hides are usually soaked from twenty-four to forty-eight hours. Dry hides require much longer. The water should be changed once or twice during the process, since dirty water may injure the hides. Soft water is better than hard for this process. Where the water is hard, it is customary for the tanner to add a quantity of borax to it to increase its cleansing power and to hasten the softening of the hides.
When dry hides have become soft enough to bend without cracking, they are put into a machine and beaten and rolled, then soaked again until they are soft and pliable. It is very important that all the salt and dirt are removed during the process of soaking, as they injure the quality of the leather if they are not removed before the hides are unhaired. When the soaking process is completed, the lumps of fat and flesh that may have been left on by the butcher are removed by hand or by a machine, and the hides are then in condition to be passed along into the next process. The parts that cannot be made into leather, such as tails, teats, etc., are trimmed off before the hides are soaked. Large hides are cut into two pieces or halves, called “sides,” after they have been soaked.
For the purpose of taking the hair from the hides and skins, lime, sulphide of sodium, and red arsenic are used. Lime is sometimes used alone, but usually one of the other two chemicals is mixed with it. The lime is dissolved in hot water, a quantity of either sulphide of sodium or red arsenic is added to it, and the solution is then mixed with water in a vat, the hides being immersed in this liquor until the hair can be easily removed. The action of the unhairing liquor is to swell the hides, then to dissolve the perishable animal portion and loosen the hair so that it can be rubbed or pulled off.
There are several different processes of unhairing the hides. Each tanner uses the process that will help to give the leather the qualities that it should have, such as softness and pliability for shoe and glove leather, or firmness and solidity for sole and belting leather. This is one of the most important in the series of tannery processes, and if the hides are not unhaired properly and not prepared for tanning as they should be, the leather will not be right when it is tanned and finished.