From the Knife Lab...
Lithographic Anodizing
For my hanova I wanted to experiment with anodizing some patterns from simple to complicated onto the titanium scales. This presented a couple of unusual challenges. The scales are three dimensionally contoured so simple masking would not work. Some of the ideas I have include more than two colors so that also made simple masking impossible. The contours ruled out dry film photoresist like you use on PCBs for electronics, it just doesn't lay well on concave areas. It also has some material limits with something like a gradient fade.
I got my hands on some liquid negative photoresist that I thought could work. In a nutshell the piece is cleaned, the base color anodized, then it's painted with the mask, a projector exposes the pattern image onto painted mask and a solvent is used to remove the unexposed areas.
Overall the final result wasn't that pretty but the experiment was a success in that it proved the technique works as a proof of concept.