Colcothar
red oxide of iron, ferric oxide, Fe2O3. A reddish-brown powder obtained when ferrous sulphate is distilled for Nordhausen sulphuric acid; it remains in the retorts. It is used as a red pigment, and is employed to polish glass, and, when finely divided, by jewelers is known under the name of rouge. It is sometimes called crocus martis, and was called caput mortuum vitrioli by the alchemists.