Originally Posted by Stepchild
wrong. PVD does not require placing any parts into an acidic bath and applying a current to them. Ti, has a different refractive index depending on the thickness of the Ti layer and by thickness I am talking on the order of nano-micro meters. Because of the difference in refractive index you see a different colors. Many different chemicals are used to supply the Ti, and the chemicals used will supply it in different proportions causing different thicknesses and in-turn the pretty colors.
That is how PVD works.
Also as mentioned by someone previously about electroplating Ti. The biggest issue with that is the face that Redox potential of Titanium is so much higher than Al that it makes it almost impossible to get a Ti layer on the outside of Al using electrochemistry.
I think what he was saying is that with PVD you could plate Ti onto Al, which you could then anodize. Which you could do, its just not aurora. PVD, its standard use, that is, would give you a very thin, very even coating. But it can be manipulated to give you an uneven coating.
And yeah, it would be very hard to electroplate Ti.