Definition: Susan Miller Cavitch, in The Soapmaker's Companion, calls "what is the white powder on the surface of my soap" the "million dollar question." Ash is a white, powdery substance that mysteriously appears on soap as it is curing - usually on the surface of the soap as it is sitting in the mold hardening overnight after it is first poured. It will usually only form on the sides of the soap that are exposed to the air while hardening.
What is it?
Some soap makers believe that it is sodium carbonate formed by the free sodium from the sodium hydroxide (lye) and carbon dioxide in the air. Susan Miller Cavitch had a chemist friend of hers test the ash once, and theorizes that it's actually microcrystalline powdered soap residue.
What do I do about it?
It's not harmful, just a nuisance. Some soapers even prefer the "rustic" look. The easiest thing to do is just trim it off with your soap beveler or planer, or just wash it off under running water. There are also ways to help prevent it:
- After you've poured the raw soap into your mold, cover it with a layer of plastic wrap to minimize the contact with the air.
- Add a bit of bees or soy wax to your soap recipe. This seems to eliminate it as well - most folks use the wax at about 1-2% of the amount of their total oils. (e.g. 1.5 oz. of soy wax in a batch of soap with 100 oz. of oils) Thanks to Cindy at Windmill Soaps for that tip.
- Just get used to it - it seems to happen most (to me at least) in recipes that have a lot of lavender essential oil in them, like the Lavender-Mint Layered Soap
