Cosmetic Clays are an ancient cosmetic ingredient that can cleanse and soften the skin. So it makes sense to add Cosmetic Clays to your soaps to make use of these benefits.
Clays such as White Kaolin Clay will make your soap feel soft and silky. Green Clay is especially good as a natural colourant for your soaps as well as acting as an exfoliant. Adding a bit of Pumice Powder to your soap will create a fantastic Gardeners Soap, which will soften your skin as well as giving your hands a good clean.
So to sum up, the clays and powders as well as adding colour will add texture to your finished soap. Do be careful when handling the clays as they can stain your hands. Best to wear gloves!