Chromium Tanning and Its Issues
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Between eighty and eighty five percent of the leather made today is tanned with chromium. A few years ago the figure was nearer 95, perhaps 98%. Some ecologists consider this trend away from chromium to be a very good thing, and a number of unscrupulous marketers have introduced the term "chromium free" leather as a green marketing tool. Most tanners and scientific observers are very disturbed by this approach.
The opposition to chromium stems from the fact that one form of chromium, hexavalent chromium, has been proven to cause cancer. This is not in dispute. What is not fully appreciated is that tanners do not use or create hexavalent chromium when making leather.
Way back in the 19th century a man called Augustus Schultz was cheated out of his share in a corset factory near Stuttgart. Disillusioned he made his way to New York where he got work as a chemist in a dyestuffs plant. At lunch in a New York restaurant he got talking with Julius Kuttner who was the manager of the Booth Tanning operations in the USA and they decided that it would be worth trying to make a leather which resisted moisture. The idea was that this would prevent the staining of corsets as a result of the rusting of the metal parts. Working partly in a tannery in Gloversville and partly with large wine glasses in New York Augustus Schultz developed "two bath" chrome tanning and patented it in 1884. This two bath process created and used hexavalent chrome, or Cr VI, as the industry knows it. Schultz's process started to be used industrially around 1890 but was soon to be superseded by another method developed by Martin Dennis in 1893. This latter process was easier to use and became the dominant tannage for leather throughout the 20th century. It does not use hexavalent chromium but rather tri-valent chromium (Cr III not CrVI) and is not dangerous nor a carcinogen.
All through the 20th century tanners have worked to refine and improve the chromium process via better uptake, less usage, comprehensive recycling, and careful management of waste. So much so that just last month at the UK leather chemists annual SLTC conference Dr Heinz-Peter Germann who gave the key note lecture said that "chromium tanning used with the best techniques can be classed as environmentally competitive". it does not use nor generate (unless grave mistakes are made in processing) any Cr VI, uses half to a third of the chemicals needed by alternates, and produces an effluent that is fully manageable. Many of the alternates being proposed on the "chrome free" basis such as aldehydes and aluminium have quite severe risks, some of which are not at all well understood yet. Many of the new non-chrome leathers also have the problem of not being very good in use and the main sector which has taken them up has been automobiles, only because some have a better shrinking behaviour in the dry, making it easier to fit panels into doors and dashboards.
Killing of the forests in the name of "natural tanning"
On the other hand the rush back to the more traditional vegetable processing has to be handled with care. Three or four times the amount of vegetable material is needed to tan leather compared to chromium and twice as much as most of the other alternates. Vegetable tans come from bark, wood, and nuts from trees and historically little consideration has been given to sustainability. The tales of damage done by tanners to indigenous forests and mangrove swamps litters history through Africa, Europe and the USA. In just a century and a half tanners wiped out the forests on much of the east coast of the USA. When tanners finally started to move even further west and north they had worked out how to remove the extract in situ and ship it instead of the bark to the tanners so the destruction moved to Latin America and elsewhere. Without question tanners using vegetable tannins today have to ask some serious questions about the suitability and sustainability of their materials. Even then vegetable tanning is not as efficient as chromium so the waste has large amounts of suspended solids in it and a lot of organic material with issues of COD (chemical oxygen demand). With vegetable tanning there is also reduced fixation of other chemicals such as dyes and oils leading to wastage and to polluted effluent.
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Science today tells us that tanning with chromium is not perfect. Yet it is not poisonous and it is as good as the alternatives and better than most. The real effort needs to put into ensuring that all tanneries around the world actually have effluent treatment available and use it. This is where the body of the leather industry would certainly unite as whether it be chromium, vegetable or other waste water it should not ever be let onto the land or into the rivers untreated. Enormous health and ground water contamination issues arise if this is allowed, and it is here where we should all be focusing our attention.
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PS for those not wanting to use chrome or vegetable tanned leathers consider SANOTAN, which won an APLF award for innovation in March and is made using a very safe metal, titanium.
www.sanotan.com
Mike Redwood
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