Caput mortuum (pigment)

Caput mortuum (Latin for “dead head” and variously spelled caput mortum or caput mortem), also known as cardinal violet, is the name of a purple variant of the iron oxide pigment hematite, used in oil paints and colorants for paper. It was a very popular color for painting the robes of religious figures and important people (e.g. patrons of arts). The name of this pigment could derive from an alchemical use, as iron oxide (rust) is the useless residue (caput mortuum) of oxidation. It was originally a by-product of sulfuric acid production in the 17th and 18th centuries and may have been an early form of the Copperas process to produce Venetian red and .