Leather ~ Environment

Chrome Tanned vs Vegetable Tanned

As a natural product leather has a lot to commend it, apart from well known arguments about the initial growth stage of the product.

Craftspeople who start using leather may wish to need know more about this natural and useful material. Chrome and Veg Tanned are frequent descriptors. In practice there may not seem to be much difference. Here are a few things I have learned. I am not expert, please correct me if I am wrong, and I will try not to lay too much emphasis on my own leanings (which do seem to be pointing one way). I am anxious to cover environmental and some usage issues.

Leathers come from animals ~ bull ~ cow ~ calf ~ goat ~ sheep ~ pig ~ and others. Vegans and some vegetarians need not read further. Crafters need to learn about he properties of these different leathers, and how they will suit their intended use. In general the bigger animals are made of tougher stuff.

After slaughter all hides have to be cleaned. The resulting gunge of fleshy tissues needs to be disposed of with respect to the environment. Chucking it in the nearest river cleans up one place, but transfers troubles downstream, or instream.

After scraping the skins clean, the hairs have to be removed. This invariably involves soaking in nasty chemicals. No other way has yet been discovered. Ditto ditto ~ see the above paragraph for disposal.

Traditionally the skins then have to treated so that the structural elements within them, that were once part of a living being, have to be preserved in a useful state. If this is not done the skin would slowly harden and also start to rot away (with associated nasty smell, and loss of strength). Compare the cellulose in the fibres of wood (a now dead vegetable, preserved to make paper) and the collagen of animal skins (preserved to make leather). The water in the collagen has to be removed. Simple drying is not sufficient. The water is chemically bound into the leather, and has to be chemically replaced by something which keeps the collagen supple and useful.

Centuries ago, maybe 80 centuries ago, it was found that the bark of trees contained chemicals that were released into water and then into skins. Given time, this worked useful wonders on the skins. The chemical was tannin - hence tanning. In Europe the most effective tree is the oak, although many others, such as chestnut, are used according to availability. The timescale for this is one of months rather than days. Modern production methods cannot afford such a waiting time, and other chemicals have been found that do the job more quickly ~ a day or two, rather than weeks.

Chromium is an essential ingredient of the "modern" tanning process, but not in its elemental state. It is a hard silvery metal, frequently used to provide a polished surface on less expensive metals. (Chrome-plated car bumpers.) In some forms, and miniscule quantities, it is an essential part of the human diet (broccoli and red wine being notable in this regard). Without going into too much chemistry the chromium we are talking about, in diet and tanning, is in the form of salts. Common table salt contains the elements sodium and chlorine.

 

 


 

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