I painted a lily on the 'casket case' for a friend's heart-shaped bass (long story....)

I first cleaned the case well, then sprayed with several light coats of Krylon Clear Acryllic (don't use the low-odour kind - leaves a foggy residue for some reason). Then painted with 'craft' acryllics (DecoArt, to be specific) and sealed again with several more coats of Krylon. It has been a few years now, and it seems to be holding up very well. Good luck and hope I'm not too late to help.