Anodization of titanium, tantalum and niobium takes advantage of oxidation to create a surface layer on the metals. The surface oxidation refracts light as different colors. These pics are from a one-day anodizing workshop where we colored titanium, tantalum, and niobium.
One way to anodize is electrolytically with a DC rectifier, the same type of electronic equipment used in electroforming and electrolytic etching.
