Caput mortuum (pigment)
Caput mortuum, also known as cardinal purple, is the name given to a purple variety of haematite iron oxide pigment, used in oil paints and paper dyes. It was a very popular colour for painting the robes of religious figures and important personages.
The name for this pigment may have come from the alchemical usage, since iron oxide is the useless residue of oxidization. It was originally a byproduct of sulfuric acid manufacture during the 17th and 18th centuries, and was possibly an early form of the copperas process used for the manufacture of Venetian red and copperas red.
Caput mortuum is also sometimes used as an alternative name for mummy brown, a pigment that was originally made in the 16th and 17th centuries from ground-up mummies, and whose use was discontinued in the 19th century when artists became aware of its ingredients.
