The word tanning comes from the Latin word tannum. In ancient Rome, a tannum was a leather maker. The verb tannare means “to make leather”.
When you think of tannins, you might think of tea or wine. If you are into woodworking, or a forester, you might think of trees. Indeed, these contain tannins, some of which can be used to process leather hides. Tanning leather is the process of removing perishable natural oils from animal hides and preserving them to ensure longevity and flexibility. The two most common tanning methods are vegetable tanning (veg tan) and chrome tanning.
Humans have experimented with methods of tanning hides for thousands of years. Ancient methods often involved animal feces and urine. Brain-tanning is one very old method that is still practiced within some Indigenous communities. It creates a soft hide that remains pliable when exposed to the elements. It is messy, smelly and labour intensive, but produces amazing results.
Vegetable tanning uses naturally-occuring tannins from plants, especially tree barks from oak, hemlock, birch, chestnut, or other trees. This process dates back to the Bronze Age (4,000 years ago). In some parts of the world, such as Northern Africa and Morocco, hides are still veg-tanned in earthen pits. Hides are soaked in water and tannin solution for several months to process the hides (historically as much as 15 months). Although it is the most environmentally-friendly method, it is becoming more rare. Approximately 10% of leather is vegetable-tanned.
Chrome tanning, also called mineral tanning, was invented in the late 1800s. Most leather today (up to 90%) is chrome-tanned. This method allows for mass-production by reducing processing time (50-60 hours). This process results in softer, more pliable, and dyeable leather.
Some leathers go through a combination tanning process. For example, after being chrome-tanned, a hide is re-tanned with vegetable tanning agents.