Caput mortuum

Caput mortuum (plural capita mortua; literally "dead head") is a Latin term used in alchemy to signify a useless substance left over from a chemical operation such as sublimation and the epitome of decline and decay (alternatively called nigredo). Alchemists represented this residue with a stylized human skull, a literal death's head.^[1]

For the pigment, see Caput mortuum (pigment).

Alchemical symbol for caput mortuum

The symbol shown on this page was also used in 18th-century chemistry to mean residue, remainder, or residuum. Caput mortuum was also sometimes used to mean crocus metallorum, i.e. brownish-red metallic compounds such as crocus martis (ferrous sulfate), and crocus veneris (copper oxidule).^[2]

References

1. Eastaugh, Nicholas (2004). Pigment Compendium: A Dictionary of Historical Pigments. Butterworth-Heinemann. p. 81. ISBN 0-7506-5749-9.
2. Liungman, Carl G. (2004). Symbols: Encyclopedia of Western Signs and Ideograms. Ionfox AB. p. 236. ISBN 91-972705-0-4. Retrieved January 20, 2023 – via Google Books.