Cold Weather and Soda Ash


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Well-Known Member
Feb 18, 2016
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So my search turned up nothing.

So here goes, the weather here in Iowa decided to change last week from perfect to cold. A batch of soap that is about 8 weeks old suddenly developed a lot of soda ash on it.

1. Is it the cold?

2. Does this mean it wasn't fully cured?

3. If I ship any soaps, can they develop ash? If so what can I do to prevent it?

I know the first part of #3 is yes.

Thank you in advance for your patience and wisdom.

Ford Prefect

Well-Known Member
Oct 24, 2017
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I can't answer your other questions, but in regard to question 2, if you are getting soda ash it means that CO2 in the air is reacting with residual NaOH in your soap to form soda ash (probably in a hydrated form of which there are three, Na2CO3-1 or -7 or -10H2O), so not all of your lye had reacted out. Interesting that soda ash combined with sodium bicarbonate and a few other trace materials was known in ancient times as natron and was one of the primary materials used by the ancient Egyptians to prepare mummies for burial. The modern symbol for sodium (Na) is derived from the new Latin term natrium which was derived from the earlier Greek term nitron, which was derived from the even earlier Egyptian term natron described above. Save that knowledge for a future trivia game.


Paladin of Soap
Oct 3, 2015
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Wyoming, MI
To help keep soda ash down try the following...

Spray the top of you soap with isopropyl alcohol.
Add a couple percents of beeswax to your recipe. (rerun through soap calculator)
Use the Cold Process Oven Process.

Please note this is not an exhaustive list. Everyone has their own methods for dealing with the soda ash issue, and I am sure they will chime in soon.


Active Member
Dec 2, 2016
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We are in Chicago, and the cold descended upon us as well :cry:

In my limited soapmaking experience, I've had soda ash developing always in the next few days after pouring / unmolding. I have had a batch developing some about 10 days after.
It seems that your soap is almost fully cured when the soda ash made its appearance. As I have no experience with that, maybe somebody else might want to chime in.

As soda ash is derived from the reaction of free sodium hydroxide with carbon dioxide in the air, the soda ash usually appears in the first few days, when there is still free lye in your soap (but up to 95% of the lye is consumed in the first 1-2 days).

Is your soda ash readily water soluble? Try to wipe it with a wet, but not dripping napkin and see. If it goes away on the first pass, then it's soda ash.

If it doesn't and you mostly brush it away (thus, it does not dissolve readily) then it might be something else. What is another deal here, so let's wait for the test before giving any comments.
It might also stay stuck to the surface of the soap.

When you noticed the appearance of the "soda ash" did you noticed also an increase in humidity in the few days before? It happened to us in Chicago, after three days of uncessant rain and drop in temperatures. All our curing soap were sweating!
The combination of cold and humidity, and concomitant lack of open windows and heating caused some of the glycerin in the soaps to draw the bountiful humidity in the air and form droplets. After we turned on the heating, they were as dry as before.

However, in our case, the few ashy soaps became perfect after this sweating issue!

Can you tell us your recipe for this soap (including water amount and lye) and which EOs/FOs you used? This might give me and others a better idea of what's going on...



Well-Known Member
Jan 4, 2015
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NW Pennsylvania
I have had soap that was almost cured develop soda ash. I was very puzzled because I know what ash is and there had been no zap for weeks! There is a thread on here somewhere about it.

I do believe cold had a lot to do with it. I don't get ash in the summer and do in the winter. I have found cpop to help as well as spraying with alcohol. Also, leaving in the mold as long as possible without creating issues cutting helps.

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