Polishing rouge; a reddish brown oxide of iron, used in polishing glass, and also as a pigment; -- called also crocus Martis.

iron (III) oxide (Fe2O3) by-product from sulfuric acid manufacture [Lavoisier

The residue produced by strongly roasting blue vitriol (copper sulfate); it is composed mostly of copper oxide. The residue from the roasting of iron vitriol (ferrous sulfate) is also called colcothar and is composed of iron oxides.