What is tanning?
Tanning is the process of substituting the water in the skin with something else that stops the skin from decaying. There are manny different ways of tanning leather. Most methodes can be used on almost all types of leather. Traditionally vegetable tanning has been most commonly used comercially untill it was mostley replaced by chromium tanning in the 1970's.
Vegetable tanning
A huge range of plant matter contains tannins. Tannins are astringents, molecules from plants that easily binds with proteins. Tannins work by tightening the pores of the skin and draws the liquid out. Tannins are usually present in plants as a defence mechanism against microorganisms like bacteria and fungi.
Tannins can be recognized by chewing on the material. When you put it in your mouth your cheeks pucker, it is experienced as a dryness in the mouth.
Most common source of tannins for tanning is tree bark.
Fun fact: Tea also contain tannins. When you drink tea (from the tea plant) the tannin will bind to the proteins in your liver and kidney, lightly tanning your insides. To avoid this you can add milk to the tea, causing the tannins to bind to the milk proteins instead.
Mostly used for commercial leather production up until the invention of chromium tanning in the 1970’s.
Here is an overview of natural souces of tannis you can use for a little home experiment.
​
​
​
​
​
Chromium tanning
​
Chromium tanning goes under the category mineral tanning. Mineral tanning is a name covering all tanning with inorganic salts, like Chromium 3 or 6, alum (aluminium sulphate, also called white tanning) or table salt (sodium chloride).
Chromium tanning is the most used method today due to its quick processing, softness and that it is less suseptable to water stains then vegetable tanned once. While vegteble tanning can take several months for bigger hides, chromium tanning can be done in one day. However, chromium tanning is somewhat less natural. First it is placed into a bath of acidic salts for the chromium to better fit in between the molecules of collagen in the hide, and then aftherwards brought back to the original pH level. The tanning itself is done using chromium 3 sulphate, a non-toxic chemical. However, if not properly mangaged it can have a negative environmental impact. In addition, Chromium 3 can oxidize into chromium 6, a carcinogenic substance which may be harmful for the workers in the factories.
​
Vegetabe tanned leathers are biodegradable, wheras chromium once are not. However, cromium tanning use less water and tanning agents. Cruomium tanning is the only one of the tanning methods mentioned in this artlicle that is not biodegradable, and it can also not be recycled. Today, chromium is used for about 90% of the commercial leather production.
​
Oil tanning
A mixture of egg, soap and oil is worked into the skin. With most animals this process should be node in a hot environment to open up the pores in the skin, however, fish skin is an exception to this as it needs to be kept under 20 degrees celsius during the whole tanning process
​
Brain tanning
The brain of the animal is cooked and then applied to the skin the same was as for oil tanning. It is said that the brain of the animal should be enough to tan the entire animal. Althoug it is one of the most disgusting sounding methods, it is also one of the most sustainable once as it requires nothing but the brain of the animal. This method can be used with fish skin as well, but not using fish brain as it is not big enough.
Other tanning methods
There are many more tanning methods than listed here, such as urine tanning, aldehyde tanning and synthetic tanning, and the list just goes on and on. This post was more to give you a short introduction to tanning, especially the methods that we use with our producs and other most commonly used.
​
Sources
Chapman, J. (2003). Emotionally durable design, Objects, Experiences & Empathy. London: Earthscan.
Hoogvliet, N. (2021). Fish Leather, by studio Nienke Hoogvliet.
Richards, M. (2022, September 15). Bark Tanning. Retrieved from https://braintan.com/: https://braintan.com/barktan/1basics.htm
Shoppe, T. W. (2022, September 15). What is Vegetable Tanned Leather? [The Ultimate Guide]. Retrieved from https://www.thewalletshoppe.com/: https://www.thewalletshoppe.com/vegetable-tanned-leather/
Storlien, H. P. (2022, Juli 18). garving. Retrieved from Store Norske Leksikon: https://snl.no/garving
​
HQ, C.(2015, August 28). Chrome vs Vegetable Tanned Leather. Retrieved from https://www.carryology.com/insights/chrome-vs-vegetable-tanned-leather/
​
Brain tanning image, 2022, Retrieved from https://wanderingbull.com/leather-types/
​
Chromium tanning image, 2022, Retrieved from https://www.sole-runner.com/en/content/chrome-tanning
