Where sapphire gets its blue tint mainly from iron, rubies get their pink to blood-red hue from chromium. So [NightHawkInLight]’s recipe starts with aluminum oxide grit-blasting powder and ...

Menzies, I. A., and Mortimer, D., Second Int. Cong. Metallic Corp., New York, 1963. Menzies, I. A., and Mortimer, D., Corrosion Sci., 5, 539 (1965).

A browse through images of chromium compounds on Wikipedia shows a whole spectrum of colours: dark red chromium(VI) oxide, orange-red lead chromate, bright yellow sodium chromate, brilliant chrome ...