Failed experiment 10cm x 10cm

Ah, yes, the moisture from the finish oxidized the copper. Try applying a clear coat to the copper, first. That might work...

Maybe a failure in the technicals, but as a painting pretty good, and as a miniature (4x4 inches in real money, for an oldie like me)...it's a very good effort.

Not really knowing, but wondering.....if you had painted it in oils maybe this reaction wouldn't have happened, not being water based I mean. Perhaps you can paint over those bits which are blue?

I don’t mind the blue I think it adds to the portrait, you don’t always have to have ‘skin colour’. However, if the whole thing starts to go blue and darkens, then that’s a different story, and how it could be rectified I wouldn’t even know where to start. I like the portrait a lot, and painting on a different surface pushes the barriers. There’s a gallery in Nottingham that is featuring an artist who paints on stainless steel, and the effect is amazing.

Thanks for your nice comments.

I think Skylar is right, and I suggest you take a look at the Natural Pigments and MITRA websites (the latter being the University of Delaware). What's happening is that the copper is (as said) oxidizing and discolouring the paint: it's not the white you're using, but the lack of preparation of the copper sheet - don't ask me how to prepare it, because I don't paint on copper and don't know. But one of those sources will know, at least about oil on copper - acrylic on copper might be a more esoteric piece of research, but there's almost bound to be something online.