nColcothar(Chem) Polishing rouge; a reddish brown oxide of iron, used in polishing glass, and also as a pigment; -- called also crocus Martis.
Century Dictionary and Cyclopedia
ncolcotharThe brownish-red peroxid of iron which remains after the distillation of the acid from iron sulphate. It is used for polishing glass and other substances, and as a pigment under the name of Indian red. Also called chalcitis, crocus or crocus martis astringens, and caput mortuum vitrioli, or red vitriol.
Chambers's Twentieth Century Dictionary
nColcotharkol′kō-thar a dark-red iron peroxide formed by calcining copperas.
Webster's Revised Unabridged Dictionary
NL. colcothar vitrioli, fr. Ar. qolqoṭar,
Ferric oxide is known as colcothar, English-Roth, rouge, crocus, etc.
"Friction, Lubrication and the Lubricants in Horology" by William T. Lewis