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...
L.