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Mike Redwood condemns the confusion created by holding outdated leather production methods over the industry’s head long after they’ve been deemed unsafe and replaced.
When I started in the leather industry in the north of England, we occasionally collected a bucket of blood from the abattoir for our black finishes.
I do not know if anyone still uses blood, but I do know that the solvents my father introduced into his tannery in the 1930s are rarely used today. Those historic solvents regularly in use 50 years ago have been replaced with safer materials in the tannery.
Later when I worked in Santa Croce in Italy, most finishing we did involved formaldehyde and many tanners around today will have worked with it for years before problems were recognised. Throughout history, we have learned new things about materials, and this is most often classed as progress.
Formaldehyde and arsenic
Formaldehyde gets a mention in Wikipedia in a section called “Tanning (leather)”: “Formaldehyde and arsenic, which are used for leather finishing, cause health problems in the eyes, lungs, liver, kidneys, skin and lymphatic system and are also considered carcinogens”. This information is referenced with a source paper published in the peer-reviewed Journal of Cleaner Production published in 2015: "Toxic hazards of leather industry and technologies to combat threat: a review".
While obtaining access to the paper, I had the opportunity to message one of the co-authors, Sumita Dixit, to ask her if the mention of arsenic really is still pertinent in the modern leather industry. She is Senior Technical Officer at the Food Toxicology Division at the Indian Institute of Toxicology Research in Lucknow.
Keeping up with the times
I do worry that this well-constructed paper has built a list of chemicals that might have been used at some stage in the past without a real check of their current utilisation. It is not helped by a list of references, most of which come from the 20th century or very early years of this century. Hardly any of the papers referenced from JALCA or JSLTC are from this century, which creates problems of credibility when the technology of processing and waste management has advanced so much in recent years.
The very fact that such a paper should provide an acceptable source for a Wikipedia article, and consequently for any group with an agenda to use to condemn leather for the continued use of arsenic and attack the “toxic sludge” of leather manufacturing, shows the risk in this area.
Arsenic has been known and used as a poison since Roman times. It also had its good uses, such as the treatment of syphilis and against some cancers, albeit it was replaced as soon as penicillin and other alternate treatments were found. It is still rumoured that Napoleon Bonaparte died of arsenic poison. Perhaps he used too much Scheele’s Green to paint the walls of his house. According to The Los Angeles Academy of Figurative Art, this was invented in 1775 by the Swedish chemist by heating up sodium carbonate, adding arsenious oxide, and stirring until the mixture was dissolved. Copper sulphate was then added as the final ingredient which ends up giving it its vibrant green colour. It became hugely popular.
The death of Napoleon from arsenic is unproven but it was removed from wallpaper in the 1840s and fully banned in green paint in the 1960s. The same with leather. Arsenic sulphide was mostly used in the leather industry to help speed-up unhairing. It was difficult to apply and expensive so, by the time I was studying leather in the 1960s, it was already in the history section, and in the U.S., Wilson had noted in his 1941 book that it had long been replaced by sodium sulphide and hydrosulphide.
The paper suggests that arsenic is used in leather finishes but, if it is found in tanneries today, it is more likely as an insecticide such as lead arsenate or sodium arsenate. Lead arsenic was used in orchards in the 1800s but was discontinued mid-20th century after health issues were found with orchard workers and there were concerns about arsenic residues on fruits. Some use apparently continued with wood preservatives and organic arsenic pesticides.
There are some important points here:
And we need to remind critics and commentators that we do not condemn laundries because for centuries they collected and used urine to get rid of the worst stains. Nor do we reject all cosmetics for their 19th-century utilisation of mercury and arsenic.
We need to maintain our honesty and transparency as do our critics, opposing the creation of false narratives based on a compilation of historic data. And remember that, in the right finish, blood can still be useful.
Follow Dr Mike Redwood on Twitter: @michaelredwood
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