Charcoal is the lightweight black carbon (C) and ash residue hydrocarbon, a non toxic pigment (PBK-7) whith excellent permanence.
It appears black because it reflects very little light in the visible part of the spectrum, It is one of the most stable and refractory of all materials.
This black pigment was used extensively as paint pigment since prehistoric times. Rembrandt, Vermeer, Van Dyck, Cézanne, Picasso, and Manet used it in their paintings.
Carbon blacks are made by heating wood or other plant materials with a very restricted air supply.
The charcoal I use the most is willow sticks, with no binders, but sometimes I used compressed charcoal as well.