The tanning of the skin is definitely one of the oldest activities of man.
The prehistoric man understood that the skin of the animals he hunted should not be discarded, but by working it could be used. Of course, the tanning process has undergone many changes from prehistory to the present day, especially from the twentieth century, when industrialization and new machinery have allowed a development in the search for specific products (once also very polluting) and a development in machinery useful for tanning and refining.
Leather and leather are still handcrafted. There are great tingeries, industries, but the skill and dexterity of the operators is what makes the skin a unique and valuable material. The skin, waste of the food industry, is "recycled" from the tinge and processed in such a way as to make it a "noble" and fashionable material. This requires increasingly state-of-the-art machinery and continuous research.
The tanning production process can be essentially divided into three major phases: tanning, reconciling and finishing.
THE TANNING OF THE SKIN
All tanning operations are used to stabilize the skin and are carried out with the use of large washing machines called coopers. The bottale is the typical tannery machine and consists of a cylinder rotating around its axis in which water, skins and chemical reagents are placed. Today, the simple rotating wooden cylinder barrel has been transformed into a complex computer-controlled machine with automatic controls and adjustments of water input, temperature, rotation speed, chemical reagents.
In this way, errors due to manual dexterity are also minimized, creating an automatic processing and a constant quality.
The operations of preparation for the tanning of leathers (which start from the raw skin) are many and we do not analyze them because they are too technical. Let's just highlight a very important operation.
At some point in the process the skins are split, that is, they are divided into two or more layers. This splitting operation is necessary for heavy cow skins, which are naturally too thick to be used in the production of artefacts; this process is carried out with a machine called a splitter in which the calcite skin is pushed by two cylinders zigzagged against a ribbon blade that cuts the skin into two layers parallel to its surface. The top layer that contains the grain (typical design of the animal's skin, outer part) constitutes the flower layer, while the lower layers that do not have the grain make up the crust.
So we also explained what the crust is. It is the lower part of the skin that is divided by the flower, the top. After this operation there are other processes that we do not go to analyze, and we arrive at the real moment of tanning that turns leather leather.
There are different types of skin tanning.
The tanning of the skin with chromium is the most widespread. You can produce any type of product except for footwear. At the end of tanning the skin is blue-green, in this state tanned leather is in fact called wet blue.
Vegetable skin tanning is the oldest, plant tannins are used that give tanned leather more or less intense brown tones. There are two types of vegetable tanning. The slow tanning in the tub, during which the skins are immersed in tanks containing tannin solutions at increasing concentrations, lasts about 30 days and serves to produce leather from very full and inflexible sole. The quick barrel tanning, made in the barrels, which due to the rotational movement, gives life to a more flexible skin suitable for all productions. The tanning takes about 36 – 48 hours.
THE RECONCICY OF THE SKIN
The skin so far tanned is not yet usable to produce items. It is in fact still wet and even if it were dried it would be a product too rigid and the typical color of tanning, certainly not with the colors that we are used to seeing. To become a commercially used product, it must undergo additional chemical and mechanical treatments: pressing:
it is a mechanical operation with which most of the water that soaks the tanned skin is eliminated. It is in fact a pressing of the skins that is carried out by crushing them between two cylinders.
Skin splitting: this can be done after the calcinaio or after the chromium tanning. The choice depends on the product you want to get.
Shaving the skin: with this operation the entire surface of the skin acquires a uniform thickness.
the reconciling, dyeing and fattening of the skin: it is the operation with which the skin is given the desired color, flexibility and softness. It is carried out in the coopers.
Skin drying: the operations mentioned above are carried out with the use of water for which the skins must be dried, a process that can be carried out for simple exposure to air, or with the use of control or in special steel plates heated and vacuumed. The choice of the drying system depends not only on economic factors but also on the intended use of the finished material.
Skin pile: The skin is softened by a machine that performs a mechanical typing.
THE REFINING OF THE SKIN
It is the final stage, but also the most complex of the processes and includes all the operations carried out on dry skin to change the surface from an aesthetic and functional point of view. Skin refining can be mechanical or chemical.
Mechanical refining of the skin: it can be done by polishing the surface with a velvet wheel, or for ironing and plating to obtain a flat and smooth surface, for pressing with a relief plate for the purpose of imprinting a print, by banging by quickly rotating the skin to have a moving surface and the flower much more noticeable.
The chemical refining of the skin: it consists of covering the surface of the skin with a film, more or less often, synthetic or natural of dyes, pearls, paints and is carried out by means of rollers, veilers and sprays.
The ironing of the skin: necessary operation to ensure the desired tone of brilliance.
Imagine the various stages of processing as a journey between departure and arrival, which an athlete must perform. It goes without saying that even if starting from the same point, if a skin makes the long path and makes some important and challenging steps, it comes to the end long after, with much more effort, with a huge expenditure of energy.
If a skin makes a shorter path or cuts along the route, skips passages, avoids difficult and expensive steps, arrives much earlier and with less energy expenditure.
That's why some skins starting from the same starting line (e.g. they are all cow skins) depending on the different paths of tanning, reconciling and refining
are markedly different from each other and with markedly different final prices.
Many operations are optional and so do them or do not do them is just a matter of cost and end result that you want to get with that particular item.