At last a question I can come out of lurkdom to answer. Although I'm
sure Elaine Luther will reply as well.
Gold PMC needs to be fired at 1830. Well above the melting point of
sterling. Even if you use it as a slip to paint over a silver bezel,
it wouldn't stick to sterling. Too much (many?) oxide(s). If you
depletion gild a layer of fine silver onto your sterling piece you
might try painting gold slip and torch firing it, but it really
sounds like traditional gold bezel would be better in this instance.
There is a great Yahoo! group for folks interested in metal clays,
both PMC and Art Clay at groups.yahoo.com/group/metalclay
Hope this helped,