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FORMS OF LEATHER

There is a number of processes whereby the skin of an animal can be formed into a supple, strong material commonly called leather.

Vegetable-tanned leather is tanned using tannin (hence the name "tanning") and other ingredients found in vegetable matter, tree bark, and other such sources. It is supple and brown in colour, with the exact shade depending on the mix of chemicals and the colour of the skin. Vegetable-tanned leather is not stable in water; it tends to discolour, and if left to soak and then dry it will shrink and become less supple and harder. Historically, it was occasionally used as armour after hardening, and it has also been used for book binding.

Chrome-tanned leather, invented in 1858, is more supple and pliable than vegetable-tanned leather, and does not discolour or lose shape as drastically in water as vegetable-tanned. It is also known as wet-blue for its colour derived from the chromium. More esoteric colours are possible using chrome tanning.

Aldehyde-tanned leather is the leather that most tanners refer to as wet-white leather due to its pale cream or white colour. It is the main type of leather used in chrome-free leather often seen in infant's shoes and in automobiles that prefer chrome-free leather.

Synthetic-tanned leather is tanned using aromatic polymers. This leather is white in colour and was invented when vegetable tannins were in short supply, i.e. during the Second World War.

Alum-tanned leather is tanned using aluminium salts mixed with a variety of binders and protein sources, such as flour, egg yolk, etc. Very light shades of leather are possible using this process, but the resulting material is not as supple as vegetable-tanned leather.

Rawhide is made by scraping the skin thin, soaking it in lime, and then stretching it while it dries. Rawhide is stiffer and more brittle than other forms of leather, and is primarily found in uses such as drum heads where it does not need to flex significantly; it is also cut up into cords for use in lacing or stitching, or for making many varieties of dog chews.

Leather – usually vegetable-tanned leather – can be oiled to improve its water resistance. This supplements the natural oils remaining in the leather itself, which can be washed out through repeated exposure to water. Frequent oiling of leather, with mink oil, neat’s-foot oil or a similar material, keeps it supple and improves its lifespan dramatically.

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