I'm always looking for ways to dress up soap, especially my hot process bars which can sometimes come out looking a bit plain. A while back, I found some scrapbooking stamps at a craft store that was closing down. The stamps didn't make much of an imprint on the soap, but I found that dusting them with a touch of mica made the shapes stand out much better.
The mica I used is called 'copper', but it really doesn't seem to have any colour to it. It's more of a shimmer/sheen.