People began to produce leather many thousand years ago. In fact, leather manufacture is one of the oldest manufacturing industries. Before that animals had been hunted only for food, but at some point of time primitive men began to remove the skin from the animals before actually eating them. There is evidence that at that period of time men used sharp flints to peel the animal skin away from the skeleton. But then people realized that to avoid rapid decomposition and decay of the skin, some skin preparation procedures should have been done. Men noticed that drying the animal skin would certainly protect them, but resulting material was rather uncomfortable, inflexible, and rough. Soon men realized that the skin should have been softened, and this could have been done by rubbing the skin with fats, which also prevents it from getting wet.
The very first method of leather tanning came as a fantastic discovery. By using various barks, berries, leaves, and water primitive men could make vegetable extracts containing liquid. When the skin was immersed in these mixtures, they were acknowledged to become rot resistant and significantly softer than dried skins. The active components of these liquids are known as tannins.
The process of leather tanning spread rapidly and was improved multifold by different nations. In the middle ages, leather manufacture processes began to be very well arranged. A lot of tanneries were established during that time, concentrated mainly in the special areas. As a rule, those areas had good sources of all necessary materials such as water supply, a lot of trees, a supply of the skin and hides, etc. Thus, all essential leather manufacture processes that we use today are generally based on the processes discovered thousands years ago by our ancestors.
Today, leather production is a fairly complex process. The key stages of leather manufacture are: preparation of leather, leather tanning, and post-tannage processing.
The preparations phase is mainly aimed at the removal of unnecessary elements to leave the pure material which gives the leather its strength. During the skin preparation, the following procedures are carried out: preservation, soaking, unhairing, liming, deliming, fleshing, scudding, and bating.
The next stage, leather tanning, is designed to stabilize the fibrous remains and to give it a lasting resistance to further breakdown. The tanning phase is the key stage of leather manufacture. To be brief, during leather tanning specific active groups in a tannin make up chemical bonds with definite active groups in the skin`s collagen. The process of leather tanning depends on different factors, such as skin`s condition, pH level, and the temperature. Tanning can be done in a number of ways, depending on the type of the tanning used.
Tannins can be classified as follows:
- mineral tannins
- vegetable tannins
- aldehyde tannins
- synthetic tannins
All listed tannins can be used either alone or in combinations.