Caput mortuum (Latin, meaning "dead head", and variously spelled caput mortum or caput mortem), also known as cardinal purple, is the name given to a purple variety of haematite

iron oxide Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. All are black magnetic solids. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of whic ...

pigment, used in

oil paints Oil paint is a type of slow-drying paint that consists of particles of pigment suspended in a drying oil, commonly linseed oil. The viscosity of the paint may be modified by the addition of a solvent such as turpentine or white spirit, and varnis ...

and paper

dye A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution an ...

s. Due to the cultural significance of its deep purple colour, it was a very popular for painting the robes of religious figures and important personages (e.g. art patrons), with its popularity peaking in the 18th and 19th centuries. The name for this pigment may have come from the alchemical usage, since iron oxide (rust) is the useless residue (''

caput mortuum ''Caput mortuum'' (plural ''capita mortua'') is a Latin term whose literal meaning is "dead head" or "worthless remains", used in alchemy. ''Caput mortuum'' (alternately called '' nigredo'') signified a useless substance left over from a chemi ...

'') of oxidization. It was originally a byproduct of

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...

manufacture during the 17th and 18th centuries, and was possibly an early form of the

copperas Iron(II) sulfate (British English: iron(II) sulphate) or ferrous sulfate denotes a range of salts with the formula Fe SO4·''x''H2O. These compounds exist most commonly as the heptahydrate (''x'' = 7) but several values for x are know ...

process used for the manufacture of

Venetian red Venetian red is a light and warm (somewhat unsaturated) pigment that is a darker shade of red, derived from nearly pure ferric oxide (Fe2O3) of the hematite type. Modern versions are frequently made with synthetic red iron oxide. Historically, ...

and copperas red.

References

{{Color shades Pigments Organic pigments Iron oxide pigments