Tanning. When the skin of an animal, carefully deprived of hair, fat, and other impurities, is immersed in a dilute solution of tannic acid, the animal matter gradually combines with the acid as it penetrates inwards, forming a perfectly insoluble compound, which resists putrefaction completely; this is tanned leather. In practice, lime water is used for cleansing and preparing the skin; water acidulated with oil of vitriol (sulphuric acid) for raising or opening the pores; and an infusion of oak bark or some other astringent matter for the source of the tannic acid. The process is necessarily a slow one, as dilute solutions only can be safely used. Skins intended for curriers, to be dressed for "uppers," commonly require about 3 weeks; thick hides, suitable for sole-leather, take from 12 to 18 months. Various modifications have been introduced into the process, for the purpose of reducing the time required for tanning, but so far with only moderate success, as the leather so produced is spongy and inferior in quality.

643. Morocco Leather

643.    Morocco Leather is prepared from goat or sheep skins; which, after the action of lime water and a dung bath, are slightly tanned in a bath of sumach, and subsequently grained and dressed.

644. Russia Leather

644.      Russia Leather is generally tanned with a decoction of willow bark, after which it is dyed, and curried with the empy-reumatic oil of the birch tree. It is this oil which imparts to Russia leather its peculiar odor, and power of resisting mould and damp.

645. To Tan any kind of Fur Skins

645.    To Tan any kind of Fur Skins. This will be found an excellent plan for tanning any kind of skin with the fur on. After having cut off the useless parts, and softened the skin by soaking, remove the fatty matter from the inside and soak it in warm water for an hour. Next, mix equal parts of borax, saltpetre, and glauber salts (sulphate of soda), in the proportion of about 1/2 ounce of each for each skin, with sufficient water to make a thin paste; spread this with a brash over the inside of the skin, applying more on the thicker parts than on the thinner: double the skin together, flesh side inwards, and place it in a cool place. After standing 24 hours, wash the skin clean, and apply, in the same manner as before, a mixture of 1 ounce sal soda, 1/2 ounce borax, and 2 ounces hard white soap, melted slowly together without being allowed to boil; fold together again and put away in a warm place for 24 hours. After this, dissolve 4 ounces alum, 8 ounces salt, and 2 ounces sal-eratus, in sufficient hot rain water to saturate the skin; when cool enough not to scald the hands, soak the skin in it for 12 hours; then wring out and hang it up to dry. When dry repeat this soaking and drying 2 or 3 times, till the skin is sufficiently soft. Lastly, smooth the inside with fine sand paper and pumice stone.