Here's an idea of the different types of tanning
Tanning Methods
There are quite a few tanning methods used to convert animal hides and skins into leather, but I’m only going to discuss a few of them. For more information on additional types of tanning processes, please refer to this article.
Vegetable-Tanned Leather
Vegetable-tanned leather has been tanned using tannin and vegetable matter. It is the only tanning method suitable for tooling, carving and forming leather. This is the type of leather used in holsters, and can also be used for journal covers, bags, purses, etc.
Chrome-Tanned Leather
Chrome-tanned leather is tanned using chromium sulfate and other chromium salts. This results in a softer, more pliable leather when compared to vegetable-tanned leather. Chrome-tanned leather can not be tooled, carved or formed. It should never be used for anything that will be in contact with metal that can rust, as the chromium salts will damage the metal finish. It’s cheaper to buy (compared to vegetable-tanned) because it’s quick and easy to produce.
Oil-Tanned Leather
Oil-tanned leather is not actually tanned with oil – it is usually a chrome-tanned leather that has been treated with oil to make it more weather resistant.