This is the decisive stage of leather processing: the chemical operation that turns putrescible hide into an unalterable material. The leather is inserted into rotating wooden drums, together with chemical or plant substances to prevent decomposition and maintain flexibility and structure. This process makes it softer and more resistant.
Adler carries out a number of different types of tanning, and the main products used at this stage of the process belong to the following categories: degreasing, auxiliary, deliming, soaking, fatliquoring, anti-mould and basifying.

Wet Blue tanning or trivalent chromium tanning: gives the leather a characteristic light green/blue colour, as the name suggests. It is the most common type of tanning, because it is easy, quick and economical. Chromium tanning makes the leather soft and flexible, and it is suitable for almost all purposes (except for the soles of shoes). Before being tanned, the leather is pickled, which aids absorption of the tanning agent. Tanning is carried out with a single bath in the drums, the rotating movement of which allows the chromium to penetrate rapidly.

Wet White tanning or aldehyde tanning: synthetic tannins and plant tannins are used, without the use of chromium. This type of tanning makes the leather extremely soft and pleasant to the touch. Wet white tanning gives the leather a white colour, allowing for excellent results even with paler shades, unlike chromium tanning.

Plant tanning: tanning method that uses tannin-based substances or plant tannins, extracts from trees, substances that are not dangerous for humans. Plant tanning, which gives leather a typical brown colour, is typically used for producing classic leather for the soles of shoes, because it offers excellent sturdiness and water resistance. Plant tanning also makes leather extremely versatile and natural, and thus suitable for use in a variety of sectors. In this case, the duration of the tanning and the amount of tannins used will vary depending on the purposes it is destined for.

Metal-free tanning: a type of tanning that uses “metal-free” chemical agents, guaranteeing low environmental impact. In order to be considered “metal free”, the metal present must be less than 1000 ppm; Adler’s has less than 800 ppm of iron. Metal-free tanning developed as a response to the gradually tightening of standards governing the presence of harmful substances in the tanning process. It is completely ecological (free from aldehydes and chromium) and 99% biodegradable. This innovative tanning process makes it possible to obtain a finished product with an impressive appearance.