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 ...

[Frankie]’s explanation of the chemistry is that the surface layer of the stainless is a transparent chromium oxide. With the heat of the laser, the calcium and chromium swap dance partners.

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 ...