Leather is a versatile fabric used in a variety of apparel and non- apparel products. One cannot think of riding a bike without a leather jacket or leather pants combined with leather gloves on a cold wintry night. Ladies love to carry leather handbags and leather lingerie is fast becoming their hot favorites. Leather footwear, accessories like leather belts, wallets, leather upholstery for sofas, automobile seats, leather shields and weapon sheathes, engine gaskets and harnesses - the list can go on but the uses of leather can never said to have exaggerated. This now so common fabric called leather has a very complicated manufacturing process. Making of leather fabric
is very different from that of other fabrics and its interesting to know this very ancient art of leather making which is being refined with time.
Sources of Leather
Leather is obtained from the skin or hide of animals. The skin of larger animals are termed as 'hide' such as cowhide or horsehide and the term 'skin' is used to represent that of smaller animals like calfskin or kidskin. Nowadays, skins of animals such as ostrich, lizard, eel, and kangaroo are also used to make leather but the commonly used leathers come from cattle, sheep, lamb, goat, kid, horse, mule, zebra, buffalo, pig, hog, seal, walrus, whale, and alligator.
Process of making Leather Fabric
There are many varieties of leather. All kinds of leathers have to pass through three main stages viz. preparatory processes, tanning and finishing processes. Sometimes surface coating is also applied to certain kinds of leathers.
When the hide or skin is prepared for tanning, it has to go through the processes such as pickling, soaking, liming, fleshing, splitting, deliming, bating, degreasing, bleaching, and depickling.
The raw hide is cleaned and soaked in acids or salts to prevent decomposition.
After reaching the tannery, it is soaked in water to restore moisture lost during salting.
It is then soaked in lime solution for removing hair, inter-fibrillary protein and epidermis.
Mechanical instruments like rollers and blades are used to remove fat, muscle and flesh from the skin.
The hides are usually composed of three layers- epidermis or the outer layer, corium or dermis, the middle layer, and the innermost fatty layer. These layers are separated or split to obtain the corium from which the leather is made.
the hide is washed in a mixture of water and ammonium chloride or ammonium sulphate to neutralize it.
the hide is treated with digestive enzymes to remove non-fibrous proteins.
Lipases are used to dissociate fat particles set in the skin.
The hide is made colorless by applying chemicals.
Depickling: The hide is put in sulphuric acid to lower the pH or the acidity gained during pickling.
Tanning converts the protein of the raw hide into a stable material which does not decompose and can be used for making end- products. For tanning different methods and materials are used. The hides are soaked in a tanning liquor which slowly penetrates through the hide. When the penetration is done to a satisfactory level, the pH of the float is slowly raised in a process called basification. Basification fixes the tanning material to the leather.
Chrome is the most common material used for tanning. Chromium salts used in this method gives pale blue color to the leather and thus it is also known as 'wet blue' leather. It makes leather water proof and stretchable.
In this method, which is also called bark tanning, the hide is soaked in a solution of bark of oak or chestnut. The leather becomes flexible but when dry, it doesn't stretch much.
In this method, fish and animal oil is used which makes the leather very soft and flexible.
After tanning, the leather undergoes different finishing processes that may include drying, softening, lubricating, dyeing and coloring. For a smooth finish, the leather may be treated with waxes, shellac or emulsified synthetic resins, dyes,
and pigments. Sometimes, glazing is done to get polished surface.
The leather is dried in the air or in a drying tunnel. Sometimes, other methods like paste and vacuum drying are also used.
Oils and greases are incorporated into the leather to lubricate it for enhancing its softness, strength, and water resistance.
Methods like drum dyeing, spraying, brush dyeing, and staining are used for giving color to leather.
Some leathers are surface coated for additional resistance to abrasion, cracking, peeling, water, heat, and cold.