I am always amazed when something that I think I understand completely turns out to be far more complicated than I first thought. The anodizing process was one of these things as, back in the day, I had investigated anodizing some of my PC components as a way of avoiding having to go through the laborious process of painting them. Of course I stopped short after finding out the investments I’d need to make in order to do it properly (something my student budget could not afford) but the amount of time I poured into researching it left me with a good working knowledge of how it worked. What I didn’t know was what it could achieve when titanium was used for anodizing as it’s able to produce an entire rainbow’s worth of colours.
The wave of colours you see the metal rapidly transition through aren’t some kind of trick it’s one of the interesting properties of how the thickness of a deposited titanium layer interferes with light passing through it. As the thickness of the layer increases the interference increases, starting off with a kind of blue colour and then shifting through many different wavelengths before finally settling on the regular metallic colour that we’re all familiar with. This process can be accurately controlled by varying the voltages applied during the anodizing process as that determines the resulting thickness of the layer that’s deposited onto the host material. In the above example they’re going for a full coating, hence why the bar rapidly flashes through different colours before settling down.
These kinds of reactions always fascinate me as it shows how things can behave in extraordinarily different ways if we just vary a small few parameters in one way or the other. It’s one of those principles that drove us to discover things like graphene which, at its heart, is just another arrangement of carbon but the properties it has are wildly different to the carbon that most of us are familiar with. It just goes to show that when you think you know science is always ready to throw you another curveball and that’s why I find things like this so exciting.
