Retanning of hides and skins

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General description

The retanning process can be carried out with the following objectives:

  • to improve the feel and handle of the leathers;
  • to fill the looser and softer parts of the leather in order to produce leathers of more uniform physical properties and with more economical cutting value to the customer;
  • to assist in the production of corrected grain leathers;
  • to improve the resistance to alkali and perspiration;
  • to improve the 'wetting back' property (susceptibility to rehydration) of the hides which will help the dyeing process.

A wide variety of chemicals can be used for the retannage of leather. They can generally be divided into the following categories: vegetable tanning extracts, syntans, aldehydes, mineral tanning agents and resins.

Emerging technologies

Continuous retanning and dyeing


This is a manufacturing technique developed in Italy to perform retanning, dyeing and stuffing in a semi-continuous unit with low water requirements. The line is made up of three different modules.

  • A roll machine for retanning and stuffing. Due to a system specially designed for the purpose, the machine facilitates the penetration of chemicals into the leather and then 'squeezes' the excess substances out of it. The special feature of the machine is that it includes a double basin for impregnation, so that leather can be processed on both sides simultaneously.
  • A stabilising chamber where controlled pressure, humidity and temperature help chemicals diffuse and fix into leather.
  • A soak-dyeing system, where leather can be dyed in a few seconds.

Both the roll machine and the soak system work in short-term washing mode: low volumes of water contain high concentrations of chemicals, so that the amount of effluents is kept low. The machines are provided with sensors to monitor the key parameters of the process (temperature, pH and conductivity) and keep conditions stable.

Status of development

A prototype was built and used for pilot trials in 2008 to evaluate the emerging technique. The results were promising.

Reference literature [133, Inquimica 2003].

Source: (BAT) Reference Document for the Tanning of Hides and Skins, 2013

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