I would just make a layered soap of black, white, and purple. In a cool shape though ~ a bubble dome, a hexagon, something like that. I use the black oxide from WSP, but I've never layered with it. Seems like Brambleberry has non-bleeding oxides and/or dyes, so you might take a peek there. oh, and to answer your question about the paint ... mine will stay on even after getting wet, but typically my testers (aka my children) like to scrape it off, so it doesn't actually last past the first use in this house!