The Process of Chromium Tanning for a Cow Hide Rug

Cow hide rugs and cow hides are increasingly popular materials in both the fashion and home leisure sectors and are renowned for their hard wearing, natural appearance and stylish contemporary look. These natural products have been used by man since time immemorial from the times when humans first killed an animal for food and removed the pelt to make clothing and materials for shelter.

Over the centuries numerous ways were discovered to make the skin more useable and longer lasting than raw hide, primarily that of tanning the hide which ensures that the skin will not decompose by permanently altering the protein nature of the skin. This process requires acidification of the skin and it is interesting to note that the Romans used human urine in the process and archaeological evidence has been found in Pompeii of urine being collected from public lavatories for just this purpose.

There are primarily two forms of tanning processes, vegetable tanning and the more modern chromium tanning which was first used commercially in 1856. The chromium tanning process produces a softer and higher quality cowhide. By being tanned with chromium salts the animal hides have a resultant softer and more uniform texture.

This tanning method consists of the following steps:

1) Soaking the hide

Raw cow hides are thoroughly washed prior to tanning where dirt, manure, blood, and some preservatives are applied initially such as sodium chloride and bactericides are removed from the skin.

2) Pickling the hide

Pickling dramatically increases the acidity of the skin to pH 3 which enables the chromium tanning salts to enter deep into the skin of hide. Salts are also added to the pickling solution to prevent the skin from swelling excessively. This ensures the hide will last for a long time and to assist this can be preserved by adding up to 2% by weight of fungicides and bactericides.

3) Tanning: Chrome tanning

After pickling, which may last for several days the ph of the solution will gradually lower in acidity which is when the chromium salts are added to the mix. To fix the chromium into the skin, the pH is slowly increased through addition of a base chemical which allows the cross-linkage of chromium ions with free carboxyl groups in the protein collagen of the skin. This fixative process ensures the hide will be resistant to bacteria and high temperature. Once finished a chromium-tanned hide will contains approximately 2-3% by dry weight percent of Cr3+.

4) Basification

The chrome salts are fixed with magnesium oxide and an antifungal to ensure the hide doesn’t rot or go mouldy.

5) This penultimate step is performed mechanically the to ensure the finished cow hide has the necessary thickness – this includes squeezing, being divided and then finally being reduced.

6) Lastly the hide is soaked with formiato-bicarbonate of sodium and synthetic oils which makes the final product soft and subtle and soft to the touch.

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