Tannin is a plant extract which combines with the protein in raw hide to form a material which will not decompose easily, i.e. leather.

It is found in nearly all forms of plant life but some plants are better than others at providing an extract suitable for tanning.

The main sources of tannin for commercial tanning are the wood, bark, leaves and fruits of various trees.

Tannin is extracted by immersing the relevant part of the plant in water and waiting for the tannin to leach out.

Examples of useful tannin sources:

Wattle or acacia bark from South Africa
Quebracho wood from South America
Mangrove bark from the tropical mangrove tree
Pine bark is used chiefly in central Europe
Hemlock bark from North American fir trees
Oak bark from older trees
Chestnut wood from France and Italy
Valonia acorn cup from Turkey or Greece
Sumac leaves from a shrub that grows in Sicily, Cyprus and Spain