Charcoal is made from twigs of willow or vine that have been heated at a high temperature in an enclosed vessel without oxygen. This process yields a solid drawing stick that produces a black line when stroked across a sheet of paper, a prepared canvas, or a wall primed for fresco.
The minute, splinter-like particles of charcoal readily crumble when spread onto these supports, producing great diversity of marks and varied richness of tone. Because charcoal particles are relatively large and the sticks do not contain a binding agent, the medium is easily manipulated with either a finger, paper, or pieces of leather. To hold the medium in place, charcoal requires paper with some texture, and to prevent smudging many artists apply a fixative to finished drawings.