The chemistry of leather

Redwood Comment
Published:  15 September, 2020
Dr Mike Redwood

The recent talks about the chemistry of leather by Dr Dietrich Tegtmeyer (which are easily found on YouTube) excellently update us in simple terms about how chemistry works and fits appropriately with the manufacture of leather. It shows that this is a complex subject, but a necessary one, and in the right hands can be a force for good in providing society with long lasting, sustainable materials like leather.

Two hundred years ago this November, Sir Humphry Davy was elected President of Britain’s Royal Society. He is famous for having used electricity to isolate potassium, sodium, calcium, strontium, barium, magnesium and boron and for working out the elemental nature of chlorine and iodine. He also invented the Safety Lamp used in underground mines to identify the presence of poisonous gases, mostly methane, and had many other discoveries and inventions in his short life.

Within the leather industry he is remembered for his studies of tanning, winning prizes for his research, and helping to open up the industry to the use of a much wider range of vegetable tannins than merely the local ones that each country had always worked with. Leather was a very important material in those days and Davy grew up with a significant tannery near his home. More significantly, he studied the process with the prominent UK tanner Thomas Poole whose large tannery was in Nether Stowey, Somerset. Davy discovered tannin in tea, in wine, and in a number of materials from India and Asia that had recently been brought back by explorers.

This was exciting as while Davy wrongly concluded that the process being used was almost as good as you could get, he did argue that it took too long, and partly because of this was too capital intensive. Oak bark is a particularly slow vegetable tanning processes, and anyway, Britain had been cutting town most of its oak trees to build ships to fight Napoleon. Poole made many trips to London to petition the Prime Minister to help keep tanners supplied with oak bark. Some of Davy’s materials, along with strong acids, started to be used to speed up tanning. This was only partial progress as it was largely responsible for acid rot, which led to huge damage in many of the top libraries in the world. It was largely responsible for a huge reduction in the use of leather in bookbinding after a thousand years of binding perfection.

Rushing through science and industry as he did, while giving enthralling lectures about science to packed crowds, a lot of Davy’s work missed essential structure and the linkages which would drive science and society forward; hence his assistant Faraday is often better recognised for his more narrow, yet more thorough, studies on electromagnetism.

Science is difficult and complex
Here is the point: science is difficult and complex. A single new discovery usually creates a host of avenues of enquiry, and there is rarely a single, simple solution going to be found to any problem that does not have some repercussions. The last few months of pandemic have highlighted this and shown the danger of both politicians and noisy commentators becoming involved.

It is the same with leather. We have had twenty years or more battling about chromium, about the carbon footprint of leather and about meat and dairy products in diets. What we know is that all these topics are difficult, and for most of the time the leather industry has stayed clear of the debate, or sadly, perhaps further confused it by sometimes promoting “heavy metal” free products despite the International Union Of Pure And Applied Chemistry (IUPAC) publishing in 2002 a specially commissioned report on the the use of the term, concluding “it has no coherent scientific basis” and no chemist or scientist should use it. They went on to say: “As another example, epidemiological studies show that chromium and its alloys can be used safely in medical and dental prostheses, even though chromate is identified as a carcinogen. Finally, it should be emphasised that no one uses the term “carbon” to refer to all carbon compounds. If they did, then “carbon” would have to be labeled as a human carcinogen since so many carbon compounds fall into this category.”

There are important lessons to be learned here for tanners to stick to the science, avoid straying into ambiguous or misleading terms, and to be very clear and transparent about all technical matters. Areas such as animal welfare, the importance of good and bad methane as defined in the new term GWP* instead of Global Warming Equivalent are more nuanced and will be harder to persuade the public about if we do not build a reputation for clarity and transparency.

The speed with which bad science gets turned into regulation is shown by California with Proposition 65 and their current plans to attack meat and dairy consumption. Both are well intentioned and yet, both are scientifically foolish, costly to industry, unhelpful to the environment, and in the case of meat and dairy consumption, likely to do actual harm to both biodiversity and climate change.

Mike Redwood
September 15, 2020

mike@internationalleathermaker.com

Follow Dr Mike Redwood on twitter: @michaelredwood

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