Mars Black is an opaque black pigment made from synthetic black iron oxide. It is lightfast and is considered nontoxic as opposed to other black pigments such as lampblack and ivory black. The later mentioned pigments are made from calcining organic material and may have traces of benzopyrene and other polyaromatics.
The chemical name for the pure pigment is ferrosoferric oxide. It contains iron in two oxidation states and it is a magnetic material.
Mars black, becuase of its opacity, light fastness, and tinting strength is the best black for acrylic paints. It is an excellent choice for an undercoat for both metallics and interference colors. Adding about 1% mars black to interference paint has a dramatic effect on the sheen and hue.
One of the neatest aspects of mars black is its magnetic properties. It has a large percentage of iron in its makeup and due to its molecular structure, it is a magnetic material. I found this out by holding a rather strong alnico bar magnet to a bottle of Dick Blick‘s Bl;ickrylic student grade mars black acrylic paint. I can see painting a section of wall with mars black then covering it with titanium white or perhaps a metallic paint. Then you would be able to glue magnetic sheets to the back of pictures and just hang them on the wall without using nails.