I’ve been colouring titanium successfully for a few years and
now I have a problem. For some reason I can only get the first
phase colours (below about 40V) any higher and the colours
become mottled green/yellow/pink.
The pickling solution I use is from Oppi Untracht (4% HFl, 20%
HCl and the rest distilled water) and the electrolyte is 5%
First I pickle the titanium untill it bubbles evenly, rinse
(under the tap) and then I anodise. It used to work - what could
have gone wrogn?!