Question: What is That White Stuff On My Soap?
Angela writes, "I have noticed what I think is a white residue and am wondering if you have any input on what this might be."
Answer: Susan Miller Cavitch, in The Soapmaker's Companion, calls it the "million dollar question." Most soapmakers, at one time or another, will find that a white, powdery film has covered their bars of soap. It's most usually on the tops or sides - those sides exposed to the air. In the soap making world, it's called "ash." People used to believe it was sodium carbonate formed by the free sodium from the sodium hydroxide (lye) and carbon dioxide in the air. Cavitch once had a chemist test some ash on her soaps...and theorizes that it's actually microcystalline powdered soap. Kevin Dunn, author of Scientific Soapmaking believes that it's just a white, powdery soap too - perhaps one fatty acid, like palmitic, not mixing well with the other fatty acids that make up the soap.
It generally forms during the first 12-24 hours after you pour the soap, and different people have different solutions for it. I knew a soap maker that added 1-2% soy or beeswax to her soap batches and greatly reduced her ash. Cocoa butter seems to have a similar preventative effect. Covering the soap with plastic wrap after you pour it, so that no air gets to it seems to minimize it as well. The good news is...that whatever "ash" really is...is that it's harmless and washes right off of the soap.
