A titanium rainbow

Here’s a video of a titanium bar being anodized…it cycles through several different colors before settling on a pinkish hue.

Ok neat, but why does it do that? Anodizing is an adjustment of the oxide levels on the surface of the titanium. The colors are caused by the interference of the light traveling through the oxide and reflecting off the shiny metal surface underneath…different thicknesses produce different colors.¹ As the voltage is applied to the metal, more and more oxide builds up, producing the color cycling even shown. Pretty cool!

1. I don’t think the color is due to Raleigh scattering, but it’s definitely a similar principle.↩

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