Colcothar

(kol'ko-thar.) [Ar.] (Chem.) An impure brownish-red oxide of iron, which remains after the distillation of the acid from sulphate of iron, and is used in polishing gla and metals. The best sort of polishing-powder, called jeweller's red rogue, or plate-powder, is the precipitated oxide of iron. [s. 204]