1911 Encyclopædia Britannica/Colcothar

COLCOTHAR (adapted in Romanic languages from Arabic golgotar, which was probably a corruption of the Gr. χάλκανθος, from χαλκός, copper, ἄνθος, flower, i.e. copper sulphate), a name given to the brownish-red ferric oxide formed in the preparation of fuming sulphuric (Nordhausen) acid by distilling ferrous sulphate. It is used as a polishing powder, forming the rouge of jewellers, and as the pigment Indian red. It is also known as Crocus Martis.