We used plain, unscented glycerin soap base for these projects (available at most crafts stores). Soap bases with natural additions, such as aloe vera, goat's milk, or olive oil, are great, too.
Fruit and Herb Soaps
Raymond Hom
Martha Stewart Living, April 2011
http://www.marthastewart.com/335074/fruit-and-herb-soaps-how-to
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