Martha Stewart Living, April 2011
Wash and dry all fruits and herbs; use whole berries, herb leaves, or citrus rinds with pith removed. Puree separately in a food processor. To make the herb purees, you may need to add 1 to 2 tablespoons water; place pureed herbs on a coffee filter, and wring out excess liquid before mixing into soap. Set purees aside.
To determine how much glycerin soap base you need, fill mold with water, then pour the water into measuring cup or bowl. Note the amount, pour out the water, then dry mold completely. Evenly coat interior of mold with cooking spray or petroleum jelly; wipe out excess.
Use dough scraper to chop soap base into 1/2-inch pieces. Microwave soap in a glass measuring cup or bowl covered with a paper towel on medium in 30-second intervals until melted but not boiling. (A double boiler can be used instead.) Add more soap pieces as needed, and continue melting. Remove from microwave, and stir until smooth.
Start with 1 teaspoon puree per cup of soap. Add more as desired. The color will intensify as the purees steep in the warm soap; stir frequently to keep soap from setting. Heavy additives may settle at the bottom, while light ones float to the top. For consistent distribution, let the soap cool (but not solidify); then stir in puree, and pour into mold.
Fill small containers 3/4 inch full with soap; for cartons, fill partially to form 1 bar at the bottom, or completely to make a block for slicing into bars. Spray surface with alcohol to eliminate bubbles. Let soaps set, 20 to 60 minutes, depending on size. Transfer molds to freezer for about 2 hours (this will help the soaps release from the molds).
Tear away cartons to unmold bars. For hard containers, pry soap away from the sides, and press bottom of container to release. Neaten soap edges with paring knife. Slice large bars into smaller ones. Use soaps within 3 to 4 months.
Assorted citrus peels, berries, and herbs
Paper coffee filters, if using herbs
Clean, dry containers, such as milk cartons, drink boxes, juice-concentrate cans, or yogurt cups
Heat-resistant glass measuring cup or bowl
Vegetable oil cooking spray or petroleum jelly
Glycerin soap base
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.