Allow the leftover pieces of the soap to dry thoroughly.
Using a spare cheese grater, grate these bits of soap into fine shreds.
Place these soap shavings onto a baking dish (better a dish made up of glass).
Set your oven at the lowest possible temperature and place the baking dish containing soap flakes into it. If you are using a gas oven, do not turn the burner on - pilot will be enough to do the job.
Allow the flakes to dry completely in the oven, checking them periodically. The amount of time your flakes will take to dry completely varies from soap to soap. Different additives used in making soaps have different moisture retaining properties.
In a blender, place twelve ounces of soap flakes, nine ounces of borax powder and six ounces of cornmeal.
Also add 1 1/8 ounces of sodium perborate to the blender and blend lightly on low pulse until you get a smooth powdery texture.
Sieve the grounded mixture through a kitchen flour strainer. Repeat this process several times and store the final mixture in a shaker.
To wash your hands with this powder soap, wet your hands and shake some powder onto them. Rub this powder gently to make lather and then rinse thoroughly with tap water.