While I am in new need of a bigger spool holder, that I am now printing, I have begun to prep for tests. Since this will all be done on the diamond head I will have to make a 3d conversion model once it arrives.
As for the ink, I will start with known good references. Sharpie/highlighter ink is a good starting point. I know both of them have a reputation for coloring plastics, and I know they are easy to get a hold of. So, they will be my first test subjects before I move on to more expensive and exotic plastic dyes.