Scientifically speaking, charcoal is a form of graphitic carbon and ash residue hydrocarbon, usually obtained from heated wood. This process removes water and other different elements from the wood itself. The charcoals available at The Ash Archive, also known as vine charcoals, are the result of burning sticks in a kiln with limited access of air.
In the arts, this material has been used for thousands of years since cave painting. Charcoal has a series of properties that makes it less permanent than other art media, which makes it a perfect tool to sketch quick drawings.