If you’ve made cold-process soap (or bought handmade soap), you’ve probably seen soda ash.
What’s soda ash? It’s the unattractive but harmless white layer that sometimes forms on the top of cured soap. There’s no one sure reason for some batches getting soda ash and some looking absolutely perfect. In fact, there are many theories about what even causes ash on soap. Some people say that its the sodium carbonate (from lye) that reacts to the carbon dioxide in the air. Some think it’s the mineral content in water. I’m not so sure about this one because I use distilled water and still can experience ash. Some think it’s just the way the soap molecules react with the air around them as they cure.
What ever causes it – it’s irritating!
A couple of ways to try to prevent soda ash is to use distilled water when you make soap. (Or if you’re using tea or coffee, make sure those are made with distilled water!) I’ve noticed that I tend to get especially heavy ash when my soap (shampoo bars, really) are made with beer. I love my beer shampoo bars though so I’m completely willing to deal with it!
You can mist the top of your soap with 99% rubbing alcohol once it’s poured in the mold and cover with a piece of cardboard.
What can you do if you’ve already got a batch with white tops?
You can totally embrace it. Yes, its handcrafted soap. Let’s just call it “rustic” . . . . Sometimes I do that but many times I have worked hard to texture or swirl the top of my soap and I want it to show! The best method that I’ve found is to STEAM it.
I just grab my trusty teakettle let it build up some good steam and hold the soap bar top-down over the steam for 5-10 seconds. I’ve found that the soap gets a bit slippery (and steam can burn!) so I hold the bar with a hot-pot holder for grip and protection. The top will be wet and shiny but dries quickly.
You can also just cut off the top – I hate wasting soap! – or try wiping it with a damp rag. But steaming works the best for me. While no method is perfect, here’s the difference on my Piece of Cake soap’s before/after pictures: