What is Vegetable Tanned Leather?
Tanning is the process of converting animal skins and hides into leather by utilizing some form of “tannin”. All leathers, with the exception of rawhide, go through a tanning process. Leather produced today is usually chrome tanned, alum tanned or vegetable tanned. There is also a relatively new method of synthetic tanning.
First, let’s cover a few basics about tannins.
What are tannins?
Tannins are yellowish organic compounds found in a wide variety of plants including the bark of trees (oak, hemlock, quebracho, chestnut, etc.), the leaves of some sumacs; and abnormal bulges on leaves or stems known as plant galls. Hot water is used to extract the tannins and make a tannic acid solution.
Tannins and tannic acid are primarily used to tan leather, dye fabric, and make ink, but they have many more applications. They give tea and coffee their color and some of their flavor. They are also used in the making of beer, wine and soft drinks. The natural presence of tannins in the bark of redwood (Sequoia) trees protects them against fire and termites. Tannic acid also helps keep iron from corroding.
There are medical uses for tannins such as in conditioning a cavity before filling a tooth, and as an anti-diarrhea treatment. Tannic acid was one used to treat poisonings from toxins like strychnine or ptomaine. One of the more fascinating effects of tannic acid is related to the skin color of alligators and crocodiles. Lighter green skin comes from algae-filled water but the animal’s skin will be darker if exposed to tannic acid from overhanging trees!
In the case of animal skins or hides, tannins change the composition of the skin fibers, causing them to become more pliable, water-repellant and resistant to bacteria. The tanning of leather permanently changes the structure of the skin so it can never return to rawhide.
About vegetable tanning
Vegetable tanning (also called “bark” tanning) is the method of converting rawhide into leather with these plant-derived tannins. There is evidence that vegetable tanning was in use in Ancient Egypt as far back as 5000 B.C. The process appears on tomb paintings dating from 3000 B.C. and was the only leather tanning method available for centuries.
Vegetable tanning takes considerably longer than mineral tanning (alum or chrome tanning). Chrome tanning (done with chemical salts such as chromium sulfate) is the most commonly used tanning method today and results in tanned leather within one day compared to vegetable tanning which can take several months. Alum tanning is done with an aluminum salt and is primarily used as lace leather.
Vegetable tanned leather is usually “aniline” dyed with plant extracts and the colors penetrate the hide completely. No protective coatings are added so it can absorb water and become rigid. It is strong, has a smooth finish, and is not very flexible. Most heavy leathers, such as those used on shoe soles, belts, saddles, gun holsters and some luggage, are vegetable tanned. Vegetable tanned leathers are the only suitable form of leather for tooling, carving and embossing crafts.
Many light leathers, such as those used in handbags and garments, are chrome tanned, because the mineral-tanning process makes them more stretchable. You may also find chrome-tanned leathers in a wider variety of colors.
Because the process is more time-consuming, vegetable tanning is more often used for high-quality, expensive leathers. It is far less expensive to produce chrome tanned leathers.
Is vegetable tanning environmentally friendly?
In general, we could say that vegetable tanning is the only “natural” form of tanning since the tannins come from plant materials instead of chemicals. Vegetable tanning is usually better for the environment; however this depends on the manufacturer and whether or not they are conscientious about how they dispose of waste water and other by-products of the tanning process.
Just because the leather was vegetable tanned does not mean you can be certain no chemicals were used. Vegetable tanned leather can be “retanned” using chromium salts (this is called “vegetable chrome retanned leather”). It would be wise to thoroughly research the manufacturer’s tanning process if this issue is important to you.
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