Making leather

Hides and skins are the raw material of the leather manufacturer or tanner. When man first used animal skins is not known. Skins, even when preserved by tanning, do not last as long as stone, pottery, metals and bone, and our knowledge about the early use of skins is vague. However, the numerous flint scrapers and bone or ivory sewing needles in our museums show that tens of thousands of years ago, in the early Stone Age, skins were prepared and used long before textiles. Nowadays, hides and skins are essential raw materials and important articles of commerce.

Any animal skin can be made into leather, but the skins chiefly used come from cattle, sheep, goats, pigs and horses. To a lesser extent the skins from dogs, deer, reptiles, marine animals, fish and birds are also used. Snakes, lizards, seals, whales, and sharks all contribute to leather manufacture.

‘Hide’ is the trade word for the skins of the larger animals such as full-grown cattle and horses; and ‘skin’ for the smaller animals, and immature large animals such as ponies and calves. Some skins are made into leather animals after the hair or wool has been removed; but the skins of the fur-bearing ‘dressed’, with the hair or wool still in place.

Most cattle hides come form South America, the U.S.A. and from Australia with smaller quantities form East and West Africa, Central America and the Sudan. Sheepskins come form Australia and New Zealand, and the best goat skins come form India, Pakistan, Ethiopia, Arabia and Nigeria.

There is usually a long interval between the flaying, or stripping, of the skin from the animal and putting it into the tannery for processing. If the flayed skins were left wet, they would go bad, just like meat; they must therefore be preserved in some way. The commonest method is salting. This involves sprinkling the skins with salt on their inner side; or immersing the skins completely in strong salt solution for some hours, after which they are drained and sprinkled with solid salt.

Slow and careful cooking of meat makes it more digestible and assists in the breaking down of the protein content by the body. When cooking vegetables, however, the vitamins, and in particular the water-soluble vitamin C, should not be lost through over-cooking.

Another method of drying is to stretch the skins out on the ground, or on frames and to dry them in the sun, or even better in the shade. Beetles and other insects eat skins and must be kept away by the use of some chemical such as D.D.T. The dried skins are called ‘crust’ leather and are sent in this form to the tanneries for the very complicated process of tanning. After tanning, only the ‘corium’ or middle layer of the skin is left to provide leather as we know it. It is to the closely knit fibre structure of the corium that leather owes its virtues of flexibility, strength and elasticity, its resistance to rubbing and its unique power of allowing water vapour and air to pass through it while resisting penetration by liquid water itself.