Wet Blue & Wet White Leather
The tanning process is mainly divided into two types: chrome tanning and vegetable tanning. The tanning of raw leather is preceded by some operations called “tanning setup operations” and consist of decalcination, maceration and degreasing. The decalcination operation, performed after the depilation of skins, aims to remove lime residues from the leather and bring it to optimum conditions for later stages: the maceration. The Maceration, on the other hand, is designed to “purify” the skin from all keratin residues, interphyrillic matter and fatty substances not yet removed.
The next stage of the production process is degreasing. In this case, the skins are subjected to this process only if they contain excess of fat; this is usually done on sheep and pig skins. The last stage before tanning is called pickling, which is done to reduce the pH of the leather in tripe before the tanning and the choice of its parameters, depends on the following tanning steps. This stage is very often performed in pickel liquor, from which it is named. Now the leather is ready for the tanning process: the purpose of this process is the penetration and fixation of the tanning material in order to achieve dermal tissue stabilization and indeteriorability. Tanned leather also increases its size, resistance to mechanical actions, chemical agents and heat.
The different types of tanning
Vegetable Tanning, performed with vegetable or synthetic tannins. Tannery materials and substances, which in the past were used to transform raw leather in finished skins, were mainly of vegetable origin. The active ingredient responsible for the tanning process is in this case the tannin, a substance that is, more or less concentrated, in some parts of certain plants: in the rind, in the leaves, in the wood or in the fruit. The intermediate product resulting from this process is the pre-tanned material called “Wet White Leather“.
Chrome Tanning. In recent times, chrome tanning has made shorter and even simpler the chemical and technological operations, with significant saving of vegetable tanning products. In addition, chromium salts are able to create a bond with the skin, which is certainly more stable than any known tanning process to date. Tanning takes place in a single bath, where the tanning fluid is made up of chromium sulphate solution, partially based on the addition of a certain amount of soda or other alkalinizing products. This operation is carried out in a drum and must be preceded by the pickling, which serves to facilitate and adjust the penetration of chrome into the skin. At the end of tanning, the skins have a light blue color (hence the name “Wet Blue Leather“) and they have a remarkable acidic reaction, which must be partially neutralized by deacidification before procceding with dyeing and fattening.
The most used techniques on raw skins are vegetable and chrome tanning. The tanning process takes place in special containers called drums, which are large cylindrical containers constructed of wooden slats held together by metallic rims. The size of these drums varies depending on the type of operation for which they are used. In order to guarantee the penetration of chemical the products, there are pegs inside the drums. These pegs have a rounded tip (to prevent damage to the skin), of a length of about 25 cm which allow, during the rotation of the drum, to drag part of the skins upwards, then let them fall back on the other, with the aim to intensify the mechanical action imposed by the rotation itself.
Mapel is today one of the largest exporters of Wet Blue and Wet White Leather
The Wet Blue and Wet White skins are part of a more complex tanning process that sees the leather crossing different phases. One of these is pre-tanning, from which we get this type of unique product that can be traded
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