Historical background
The day a prehistoric man realized that he could use the skin of an animal he had killed to get food to protect himself from the cold and bad weather, the fascinating adventure of leather processing began.
We can all identify the traces of this adventure over the millennia: from the leather clothes of the Similaun mummy, to the Jewish tanners mentioned in the Holy Scriptures, to the Eskimo kayaks covered in sealskins, just to name a few easy examples.
Raw
Materials
The skin that humans use can be obtained from most mammals, as well as from amphibians, fish, reptiles and birds.
The most common leathers are those of waste from the food industry: bovine, goat, and pork.
Cowhides are particularly appreciated for their characteristics of size, strength and versatility: starting from these, finished products are suitable for many uses, from footwear, to leather goods, to furnishings.
It goes without saying that cows are not raised to produce skin…
Processing
We can divide leather processing into three major steps.
The first involves the preparation of raw hides for tanning, through the so-called “river works”, which were once carried out on the banks of rivers by throwing the processing waste directly into the water.
The second phase includes the actual tanning, mineral or vegetable, followed by retanning, dyeing and fat-liquoring: the area in which these processes are carried out is called the “wet department” due to large quantities of sewage that, especially in the past, they stagnated on the floor.
The last phase, from drying to finishing, aims to ennoble, improve and protect the leather from external agents and is performed, unlike the other phases, in “dry departments”.
Quality controls
To verify the quality of the processes carried out on the hides, it is necessary to carry out a series of laboratory tests that allow to give an objective judgment on the hides and to compare different batches, different articles, different productions with standardized control methods and with reference values the same for all.
For each type of use of leather, different parameters are envisaged with regard to chemical contents, dimensional characteristics, physical / mechanical resistance and reaction to fire.
Finished leather
Leather, by nature, is not homogeneous but changes from one point to another regarding to resistance, compactness and elasticity.
It also has a number of imperfections and natural features on its surface such as scars, wrinkles, insect bites and veins.
One of the effects that you want to achieve with the various transformation operations is precisely the reduction of variations between hides and between different areas of the same hide,
both mechanical and in appearance, but no matter how hard you make it is not possible to completely standardize the entire surface.
This unevenness is a characteristic of the leather that makes its processing more complex than a fabric.
On the other hand, what makes leather easier to work with than a fabric is its near-isotropicity, that is, its resistance and elasticity almost equal in all directions.