In order to increase the penetration of the tanning agents, the raw hide undergoes a process of preparation, which may include dermal relaxation and partial saponification of the fats. Another typical step is liming, where hydrated lime (a basic agent) is added to remove any hair left on the outer surface of the hide.
The lime, together with all the impurities, is discharged during the purge. Here water and weak acids are added to lower the pH to the isoelectric point of the collagen (the protein that is then treated during the tanning process).
The final preparation step is pickling, where the hide is treated with a water based solution of salt and acid (sulfuric or hydrochloric). Reaching a very low pH is essential for the penetration of the tanning agents.
The tanning process is essential to leather production because it prevents organic degradation and gives the leather its resistance to mechanical stress and chemical agents. The most effective tanning agent is chromium(III) sulfate, and chrome-tanned hides and skins take the name of wet blue, because of the light blue color given to the product by this treatment.
The tanning process takes place in the drum, a slowly rotating hollow cylinder that can be opened and closed, where the hide is treated with a solution of the required chemical reagents (tanning liquor).
During the tanning process, the skin is brought back to its original thickness, which had been altered by the various steps of preparation. In order to obtain a uniform thickness, the product undergoes a process of wet shaving once the tanning is complete.
The tanned and shaved skins are then separated and dried on a roundabout chain where the product remains for about half a day.
Once the skins have been dried, they are selected, divided, catalogued and stored. This makes them immediately available for orders. Whenever an order is placed, the desired finish and color is agreed upon and then the dyeing process takes place in smaller drums in a matter of a few hours.
Once more, the skins are dried in a controlled environment at 35°C – this process takes about half a day. To avoid folds and creases, the skins are hanged on clamps.
This final step is meant to give the desired finish to the leather product and to improve its resistance to wear and tear. Finishing might include all sorts of mechanical and chemical processes combined to enhance smoothness or gloss, to give a worn-out look, etc.
Here are a few of the available options:
Volanatura: the leather is placed in a rotating drum (without any water) in order to enhance softness to the touch.
Dry Shaving: meant to give the leather a specific thickness.
Spraying: this can be machine-made or hand-made, according to the quality of the required treatment.
Hand buffing: allows the color to penetrate deeper into the scales and natural creases of the leather.
Discoloration: further treatment can remove part of the uppermost layer of color and give the leather a worn-out look.
Painting: bespoke treatment as agreed with the customer. All sorts of patterns or effects can be achieved.