COLORING OF TITANIUM SHEETS
Titanium, when subjected to a voltage of sufficient order while immersed in a strong electrolyte, will grow a thick, transparent oxide film. As the film thickens by just a few molecules, colors shift across the spectrum through light interference. For instance, at 10 volts, an 18 picometer-thick (there are a billion picometers in a millimeter) film develops. Pale gold in appearance, this is nearly twice the oxide thickness that develops naturally on the surface of titanium sheet. As the voltage is increased, the color changes from golds to violets, blues, oranges, reds, and greens — all across the color spectrum, albeit pastel in tone.
Titanium can be expected to remain consistent in color for decades, as it has a high resistance to compounds in the atmosphere that can discolor the surface. Discolored titanium, when it occurs, is usually due to the formation of titanium carbide, TiC, below the surface of the oxide. This should not occur under most applications. It can, however, be generated from the mill process. The appearance is a dull, blotchy reflectance in relation to surrounding surfaces of titanium. Interference colors are unique for titanium and differ significantly from the colors produced from stainless-steel interference coloring, and also differ from the possible colors in titanium-coated stainless steel (see below).