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There have been a number comments from people in the leather supply chain since I wrote a few weeks ago that chromium tanning is in permanent decline (click here to recap). This was based on the fact that the crescendo of attacks being made against it have gone on so long and been so loud that user opinion can no longer be retrieved however hard the industry tries.
Most tanners think the loss of chromium in leather making will be an error. Generally speaking, chrome tanning makes the best leather and when properly managed is environmentally sound. As Dr H-P Germann said in his 2008 Procter Memorial Lecture:
“In practice, it is safe to assume that chrome tanned leather produced in accordance with the ‘best available technique’ principle - including all environmental measures - can be classified as environmentally compatible.”
One of the difficulties with chromium, however, is that if it is not well managed it can cause problems and at the end of life of an article it can be difficult to handle. Especially if, as with footwear, it is hard to separate into its components and will just end up in landfill. That is why the Vice President of Tannery Operations at Wolverine Leathers, Sylvain Bussiere, has developed an alternate for its famous pigskin leathers. Interviewed by Richard Smith of fair organisers, APLF we are told; “Sylvain’s objective is to produce chrome-free, environmentally friendly shoes that can be disposed of when worn out without leaving chrome deposits in the land”.
The question that arises is what should chromium be replaced with. Over the last few years chrome free leathers (FOC) have been developed mostly for the automotive industry based upon what has become known as a wet-white pre-tannage. This has often involved starting with glutaraldehyde tanning agents (partially modified) or tetrakis (hydroxymethyl) phosphonium sulphate (THPS), along with mixes of polyphenols (vegetable and syntan tanning agents) and other organic-synthetic retanning agents. Aluminium, titanium and zirconium also get regular mentions. It feels a bit like the late 19th century when the bicycle was evolving and there were a multitude of designs and technologies presented. Quite suddenly they all merged into the standard triangular frame which lasted unchanged for 100 years. We know a new robust tannage is required but are not quite sure what it will be. At the moment, for footwear, many of these “chrome free” processes do not give very good leather, and require compromise in the styles and constructions for which they are used.
Traditional vegetable extracts
Currently, I am impressed by the work going on in the traditional vegetable sector to improve their materials and the different leathers that can be produced with them. Some outstanding results have been achieved with olive leaves as well as with much older materials, and the big move of recent decades to sustainable forests for vegetable extracts has transformed our view of them. For something with outcomes closer to a chrome leather look for titanium. It was rejected when first re-examined in the 1990s but more recent work has shown that this can be a very clever tanning material with a clutch of useful properties. I have had the chance to see this leather developed in the last few years in one European tannery and have been greatly impressed.
Whatever you go for, remember that it is all chemistry and needs careful planning. Having used chromium for 100 years we know about its problems and some of these other materials we know much less about.
“I will retire when I can eat my shoes”, is what Sylvain Bussiere told Richard Smith, and he will know that to be injured in any way by hexavalent chromium he would have to eat two pairs as it is only by ingestion that Cr (VI) does harm. He needs to be sure to check the alternates carefully.
Dr Mike Redwood
Follow Mike Redwood on twitter: @michaelredwood
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