For majority of us, the first thing that comes to mind when we hear the term "leather" is that it is animal skin. For the most part, we would be right. But, we also learn in our science classes that these animal skins will decompose over time unless it undergoes sort of treatment. In the leather industry, this treatment process is known as the "tanning process".
The animal hides are first dehaired and thrown into a giant drum -- think a huge washing machine -- where it is soaked in water and tannins. There are tons of ways of how you can tan leather but the more common ones these days are "Vegetable Tanning" and "Chrome Tanning".
Vegetable Tanned Leather
Vegetable tanning gets its name from its use of vegetable tannins. Vegetable tannins are made out of natural ingredients such as tree barks, chestnut shells and sometimes even dried leaves. These mixtures are then pounded into a powder form and will be used in the vegetable tanning process to transform these the "animal skins" into "leather". The different ratios of these ingredients mixed together will give the leather it's structure and colour.
Chrome Tanned Leather
Chrome Tanning on the other hand uses a type of chemical or metal known as chromium sulphate. Chrome tanning has resulted in exotic leather such as Alligators, Crocodiles, Snakes, Ostrich, and Lizards being made possible. Through chrome tanning, these exotic leathers are made pliable and usable as compared to vegetable tanned leather. To simply put, if we were to try to tanned an Alligator leather using vegetable tanning process, it will make the Alligator skin too stiff and hence, crack. However, chrome tanning is not limited to exotic leathers. More common leathers such as cow, goat, buffalo and horse are also chrome tanned and are typically cheaper than it's vegetable tanned counterpart.
Here is a short clip on how leather is made.