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.

As a side note, Mars Black 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.

Among black pigments, Mars Black is one of the better driers in oils. Mars Black is a solid, durable pigment choice which comes in various grades depending on the particle size. Normally the consistency is very smooth, but natural versions tend to be grittier. Vasari's French Ivory Black has a different texture as it is made of "Natural Black Iron Oxide and plant based charcoal." So even though they call it Ivory Black it actually contains PBk11.

Samples of Mars Black such as Williamsburg's German Earth have a visible texture. 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.

As a pigment for painting, PBk11 has quite a few advantages. Mars Black doesn't take as much oil to make a paint as some of the other major black pigments (for example Lamp Black) and it also has better drying properties.