Soda Ash is not Soda Ash

Soda ash is another name for white chalky coating of homemade soap, that looks like mold on Camembert cheese.

Soda Ash Coating

This harmless wonder presents a challenge especially for makers of soap who also sell it.

This powdery layer of uncertain nature is believed to be soda ash or sodium carbonate synthesized by a reaction of sodium from lye and carbon dioxide from the air. It’s not.

Soda ash is not soda ash at least in my homemade soap.

Soda Ash in not Soda Ash

A simple vinegar test proves it.

Vinegar Test for Soda Ash on Soap

Perhaps you know that a chemical reaction between vinegar and baking soda produces bubbles. Some cake recipes require to mix vinegar and baking soda instead of using baking powder. Many of you might have done it.

Just like baking soda and baking powder, soda ash also produces bubbles when mixed with vinegar.

The chemical reaction is very simple.

Acetic Acid + Sodium Carbonate –> Sodium Acetate + Water + Carbon Dioxide

2 CH3COOH + Na2CO3 –> 2 CH3COONa + H2O + CO2

Carbon dioxide is the culprit behind the bubbles just like in carbonated drinks or Alka-Seltzer.

To demonstrate the bubbles, I have white vinegar in one spoon and soda ash in the other spoon.

Vinegar and Soda Ash

The picture below shows the bubbles when soda ash is mixed with vinegar.

Soda ash reacting with vinegar

And now let’s do the vinegar test on the soap with “soda ash” on it.

Vinegar on soap with soda ash

I actually inundated my soap bar with vinegar, but it ran off before I had a chance to click my camera. As you can see from the puddle in the left corner of the picture above, this white substance on soap does not make any bubbles when it’s in contact with vinegar.

Ok, may be there is some film that separates soda ash from vinegar? I am going to scrape off some of that white substance and put it into vinegar.

Here is my vinegar. This time, I poured it in a clean, empty, plastic spice jar.


And here are the shavings of the white stuff. No, not the snow. Even though we’ve got plenty of it outside. Let’s call it “soda ash in question”.

Soda ash in question in vinegar experiment

I took these shavings from different parts of the soap.

Quite frankly, these shavings look and feel just like soap. Here they are, in the vinegar.

Soda ash from soap in vinegar

If you see any bubbles, they are incidental individual bubbles or air introduced when the shavings were falling down into the vinegar.
There is no foam, no bubbles, and no Alka-Seltzer effect.

After a few minutes of vigorous shaking, I’ve got this mucky suspension.

Soapy soda ash in vinegar - milky suspension

A little more shaking dissolved the rest of the stuff.

And one last thing. It smells and tastes like vinegar.

Soda ash and vinegar solution does not taste acidic. It’s actually a little sweet because you are tasting sodium acetate and not acidic acid.

My conclusion is that soda ash on my homemade cold processed soap is not soda ash. I think that I have to agree with Susan Miller Cavitch. She wrote in her book “The Soapmaker’s Companion” that this layer is most likely composed of recrystallized soap molecules that were dissolved in moisture of the air and dried.