LEATHER TANNING 

ORIGINS OF LEATHER

There is evidence to suggest that leather has been in use since the time of thE Neanderthals. Despite the emergence of this material predating science, the way in which a hide becomes leather is very much based on chemistry.

To begin with, the skin of an animal, also referred to as the pelt, is prepared for the tanning process by removing any remaining tissue or hair. What is left is called the hide. The hide is made up largely of collagen and the process of tanning is a chemical reaction between this collagen and tannic acid. Tannic acid is found in tannins which are found throughout nature. A chemist may describe a tannin as astringent, meaning it removes moisture and tightens skin cells. In the tanning process, the hide is soaked or coated in a tanning liquor. These can contain varying strengths of tannins; a well-versed craftsman is able to create the desired type of leather by concocting the right tanning liquor.

Arguably, the oldest tanning method we are aware of, is brain tanning. Fairly gruesome by today’s standards, the brain of an animal is boiled along with other ingredients to create the tanning liquor. We know today that it is the lecithin’s found in the brain that act as the tanning agent. There are accounts of this method being used in prehistoric times in various places around the globe, including the Americas, parts of Asia, southern Africa and eastern Russia. It was a labour-intensive process but created a material that was crucial for survival in the colder months.

ps: there is an animation of the Brain Tanning Process on our Instagram  IGTV page for the curious among you.

Another method is what we now refer to as vegetable tanning. ‘Vegetable’ alludes to any plant-based material, not exclusively vegetables we have in the fridge. The most common material used for vegetable tanning is bark, as it tends to have high concentration of tannins. For example, bark from oak, fir, willow, chestnut, birch, and alder trees can be used. There are lots of other sources of tannins like sumac leaves, pomegranates and acorns to mention just a few. As such a long-standing technique, there is ample literature about tannin concentrations in trees, fruits, nuts and roots.

This technique found popularity across Europe and north Africa, with the earliest example found believed to be from Ancient Egypt. In the late Middle Ages, leather was widely used, and the production became well organised. The process was split into three specific guilds: skinners, tanners and curriers. Skinners were the only people allowed to deal with fresh skins; they prepared them for the tanner. The tanner soaked these hides for up to a year, depending on the tanning liquor and type of hide, and were finished by the currier.

This method of tanning, adapted to the modern world, is employed to create the leathers we use at The Backward Vendor. The hides sourced are by-products of the meat industry and as everything that goes into vegetable tanned leather is natural, when it eventually degrades, nothing harmful will be released into the environment.

In 1858, after very little intervention for hundreds of years, the tanning industry saw a massive shift. Chromium tanning was invented, a chemical process that alters the molecular structure of collagen. This process overtook vegetable tanning in popularity as hides were made into leather in just one day. In the modern day, we can identity that a product made in a quick chemical process such as this is likely to have damaging consequences. However, this is still the most popular process of tanning today, having severe effects on the environment and the health of the people producing it.

One study estimates that for each piece of chrome tanned leather, 2-3kg of chrome shavings are produced. Both solid waste and wastewater are being dumped into local reservoirs, polluting the water - water that is fed back to the drinking supply of people and livestock. Although regulations have been put into place in some countries, many chrome tanned leather producers continue to pollute the environment.

REFERENCES

http://www.braintan.com/articles/history/history.html
http://www.braintan.com/barktan/1basics.htm
https://animals.howstuffworks.com/mammals/deer-tan-own-hide1.htm
https://www.tandfonline.com/doi/full/10.1080/193382410037308