Mars Black is an important artist color which is actually, strangely, magnetic. It is reported to have excellent lightfastness. Technically Ferroso-ferric oxide, this can be thought of like a black earth or Black Iron Oxide. It sometimes contains manganese black, so keep that in mind as far as the health risks associated with manganese - see the Artist's Guide to Health and Safety for information about the hazards associated, as she notes it is sometimes mixed with PBk14, Manganese Black. Her updated work can be found through her site.

There seem to be a few naturally occurring pigment sources, which have the nice effect of softening the intensity of Mars Black just a little - otherwise this is a powerful pigment. A couple of benefits are that it doesn't take as much oil to make a paint out of Mars Black as it does out of a Lamp Black and has better drying properties.