All the tanning processes go through these basic processes. They are important because they enhance and improve the transformation of skins and hides into leather. The preparatory processes include slaughtering of the animal, soaking, fleshing/ defleshing, dehairing, bating and pickling.
1. Slaughtering of the animal:
The leather preparation process begins with the killing or slaughtering of the animal. The skins or hides of the animal is peeled off or removed. This process is termed as Flaying. The pelt is hanged for the liquid in it to drain off. It is then dissolved in heavy salt or brine solution. This process is referred to as Curing. It is done to prevent the skins and hides from bacteria and other insect attack or decay.
2. Soaking:
The pelts are soaked in paddle vats filled with water added with chemical wetting agents. This helps in restoring some of the natural moisture lost during the curing process. It also makes the pelts soft and improves its aesthetic appeal whilst disinfecting it from further insect and bacteria attack.
3. Fleshing/ De-fleshing:
This is the removal of the excess flesh, fat and muscle found on the fleshy side of the pelts. A special fleshing machine equipped with cutting blades and rollers scrapes away the flesh from the inner side of the leather.
4. De-hairing:
This is the removal of hairs from the surface of the leather from the grain side. This is done by both chemical and mechanical means. Depilatory chemical agents like lime solution destroy the hairs by attacking the hair roots. It also loosens the epidermis and removes certain soluble skin proteins that lie deeply embedded within the skins and hides. Finally, they are subjected to the de-hairing machine that removes all the hair through a mechanical rubbing procedure.
5. Bating:
This is the process of removing all residues including those of the chemical agents used in the de-hairing process as well as the hair particles deeply entrenched in the surface of the skins and hides. Three processes are involved in the bating process. The skins and hides are first washed in a lime solution. Secondly, they are soaked in a bate solution (bate is similar to enzymes found in the digestive systems of animals). Thirdly, they are then finally re-washed thoroughly to remove all substances on the leather.
6. Pickling:
This is the final preparatory stage before tanning. It conditions the leather to receive and absorb the actual tanning agents. The skins and hides are submerged in a solution of Sulfuric acid mixed with common salt. This process helps in preserving the skins and hides, keeping them chemically balanced while preventing them from swelling.
