In article ,
Steve writes:

You don't have to go all that thin to get interference - also works with
smooth anodised aluminium.

True, I think it must be related then to the natural lustre/colour of
the metal, you certainly get stronger contrasts in Ti.

With anodised aluminium, it is a synthetic dye adsorbed onto the
surface that gives it the colour, effectively a lake. (q.v.)
Anodised titanium works on film thickness, but is fairly
complicated to achieve a predictable colour without a lot of
(expensive) trial and error. Current, duration, electrolyte and
so on all have an influence. Had I realised this was the path you
were going down, I'd have suggested (DIY ideals notwithstanding)
that you buy the stuff ready coloured.

John Schmitt


--
If you have nothing to say, or rather, something extremely stupid
and obvious, say it, but in a 'plonking' tone of voice - i.e.
roundly, but hollowly and dogmatically. - Stephen Potter