The basic component of the skin is collagen, resistant substance, belongs to the group of scleroproteins, characterized by mechanical strength and insolubility in the aqueous environment. In addition, it includes other proteins, fats and carbohydrates. Rawhide is not suitable for wares due to its lack of rot resistance. Therefore, the leather is subjected to the tanning process, which gives it new features, such as flexibility, waterproof etc. Tanning agents change the leather's ability to swell and provide properties, which are necessary for the production of utilitarian and decorative products.
Leather subjected to the tanning process changes its composition depending on the means and methods used. Among other things, the water content in rawhide drops from 65-75% to approx 15% in tanned leather. The same is true of minerals, lipidami, carbohydrates. However, it should be remembered, with different tannins (natural and synthetic organic compounds, as well as mineral chromium compounds, clay, iron and zirconium and non-metal salts), and tanning methods, give the skin different properties.
Although tanning is an indispensable process, it is also a factor that damages the skin. During tanning, there may be. mechanical damage or chemical damage, caused by using the wrong chemical composition of the bath (e.g.. excess acids, which causes the instability of the basic component of the skin tissue - protein. Simply put, tanning changes the skin's collagen properties.
Fat content. The fats used to preserve leather have a great influence on the elasticity of its fibres, and also to reduce water absorption. increasing tensile strength and elongation. The experience of conservators clearly shows, that leather goods were constantly cleaned and greased.
Too low a fat content causes the skin to lose its elasticity (the term refers to the ability of the fibers to move without damaging them) and accelerates its drying. proper, the limited fat content gives the skin resistance to elongation and contraction of fibers (caused by constant fluctuations in relative humidity), protecting it from the resulting damage and breakage. Excess fat in the skin is also harmful, m.in. reduces the ability to absorb moisture.
The content of fat in the skin depends on its intended use and varies within limits 1,5 do 12%. It is accepted, that healthy vintage leather should contain approx 3% fat.
