We call these SPA bars. They are also called salt bars. The oil used is 100% coconut, and you add about 1/4 as much salt at trace. For instance, if you used 4 pounds of oil, you'd add 1 pound of salt. The salt makes the bar harden within a couple hours, and it has a creamy lather.
My sister is WAY into beading (www.torchsongstudio.com and torchsongstudio.blogspot.com) and that inspired our packaging. Of course the batches were tiny - only 8 bars, so that helped :-).
