Chromium-based tanning agents
Metal salts containing chromium, zirconium, aluminum, titanium or iron also have a good tanning action and form very stable compounds with proteins. Of the mineral tanning agents, only trivalent chromium plays an important role and is used in 90 % of all leathers that are tanned world-wide. Chromium sulfate has been used as a tanning agent for more than 100 years. Chrome-tanned leathers are more resistant and softer than those produced by other tanning processes as a result of the particularly complex cross-linking with the skin proteins. In addition, they are heat-resistant, sweat-resistant and excellently dyeable. It is essential to distinguish between trivalent chromium which is used for tanning and hexavalent chromium which is toxic and, however, no longer of importance for tanning.
Trivalent chromium, on the other hand, is an essential trace element in our body. It is found in concentrations of 0.03 to 0.1 g/kg in our soils, rocks and vegetables. Cowhide leather of about 5.5 m2 in size contains 80 grams of trivalent chromium, i.e., about 20 g/kg of leather. Although it is treated with much distrust as a heavy metal, there has been no scientific evidence for the actual negative impact of chrome tanning on the environment or human health to this day, and this is after 100 years of successful chrome tanning. Chrome-tanned leathers tend to be soft and are therefore mainly used for shoes, clothing and furniture.