http://www.treehugger.com/files/2006/08/how_to_make_you.php#perma
1 cup baking soda, in a medium sized mixing bowl
1/2 cup liquid castile soap
5-10 drops of antibacterial essential oil, such as lavender, tea tree or rosemary (optional)
Procedure:
1. Pour baking soda into a medium size bowl.
2. Add soap a little at a time, stirring continuously, until your mixture has begun to resemble frosting.
3. Mix in drops of essential oil.
4. Store in an airtight jar for up to a year.