Batch of six bars curing on a wire rack in a spare room. At about week three, four of them developed a fine white powdery crystalline layer, mostly on the top face, patchy rather than even. It brushes off with a dry cloth but comes back within a few days. The bars lather normally. What is this and does it mean something is wrong with the batch?
Worth saying explicitly since it worries beginners — a bar with ash is completely safe to use. It's the same compound as washing soda and it rinses away. Plenty of people just don't bother removing it on bars for their own use.
Room temperature matters more than people expect. A cool room during the first 48 hours makes ash much more likely because the batch doesn't gel. If your spare room is unheated, that's probably your driver.
It's the coldest room in the house, so that fits.
Do plane rather than steam if you want a really clean face — a vegetable peeler or a soap planer takes off a paper-thin layer and gives a matte finish. Steam can leave a slightly glossy patch on some recipes.
If you want to eliminate it entirely, a slightly higher water discount and gelling in a warm oven at the lowest setting for an hour then off overnight will do it. Slightly more advanced, works reliably.
@conditioner_lab · 7mo ago · 3 replies
That's soda ash and it's cosmetic. It forms when unsaponified lye at the surface reacts with carbon dioxide in the air, producing sodium carbonate. It doesn't affect how the bar performs, it isn't dangerous, and it stops appearing once the surface has fully cured.
The reason it's on the top face and patchy is that the top is exposed to air while it's still soft. Prevention for next time:
To remove it from bars you already have, a quick pass under running water with a cloth, or a steam from a kettle held at a distance, takes it off permanently once the bar is cured.
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@conditioner_lab · 7mo ago
Lye pockets look and feel quite different — wet, sometimes slimy, and they'll zap on a tongue test. A dry powder that brushes off is ash every time.
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@wild_ferment · 7mo ago
Steaming worked and it hasn't returned after a week. Thanks — I'd convinced myself it was lye pockets.
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