Marla Bosworth is the founder and owner of Back Porch Soap Company. She teaches classes, corporate events and experiences including candle making, soap making, organic skincare and perfumery.

April 03, 2017

How to Prevent Soda Ash on Your Cold Process Soap Bars

Soapmakers generally end up with soda ash forming on their bars at least once in their soap making endeavors. Let's take a look at soda ash, what it is, way to prevent it from happening, how to get rid of it when it occurs, and an example of how it can enhance your soap.

What is Soda Ash?
Soda ash is the common name for sodium carbonate. It's a harmless, white powder that can naturally occur on bar soaps as a mineral deposit. It forms when sodium hydroxide (lye) and air (oxygen) come in contact with each other (see below on how to prevent this from happening).

Sodium Carbonate
Na-= sodium hydroxide
O = oxygen
Here is an example of a soap with soda ash (left) and one without (right). Thanks to my friend and colleague, Angela Carillo of Alegna Soap for sharing this example. The bar on the left had been exposed to air during the first 24 hours of saponification, while the bar on the right was not exposed.

Heavy soda ash on the surface of the left bar.
Photo credit: Angela Carillo of Alegna Soap

When Does Soda Ash Occur?
As in the example that Angela provided, this soap set up with soda ash during the period of 24 hours after pouring the soap into the mold. During saponification, or the first 24-48 hours and occasionally a few days into the curing process.

How to Prevent Soda Ash
The easiest, most proactive way to prevent soda ash is by reducing the water content in your soap. I haven't gotten soda ash for 15 years, and I soap at a 38% lye concentration (do not confuse this as water as percentage of oils). This is convenient if you are making soap that you want to set up quickly.

However, if you want your soap to set up slowly such as in the case of swirling or creating intricate color designs, then you won't want to reduce your water content as the soap batter will thicken too quickly on you.

Some people say that spraying isopropyl alcohol (rubbing alcohol) on the soap right after pouring into the mold will prevent soda ash. I've never found this to be true. The theory is that the alcohol helps remove the extra water on the surface layer of the soap. Give it a try and experiment for yourself.

The second best way to prevent soda ash is by simply covering your freshly poured soap AS WELL AS your freshly cut bars with a loose layer of plastic. You can use plastic wrap, a clean trash bag or a plastic table cover. Keep the plastic over the surface of the soap in the mold. After you have unfolded and cut into bars, cover again for 48 hours. If you are using full water content (lye concentration of 28%), then you may want to keep the plastic over the bars loosely for a week.

How to Remove Soda Ash
Here are some ideas to removing existing soda ash from your soap bars:
  • Wipe a damp paper towel over the bar.
  • Use a steamer to remove the soda ash (yes, some people actually do this).
  • Run the bar under water and let dry (wear gloves as this tends to leave fingerprints).

Embrace Your Soda Ash

Soda ash on the top of activated charcoal soap.
Photo credit: Angela Carillo of Alegna Soap
Soda ash can create interesting contrasts in intricate soap designs, as in the one pictured above. Again, a perfect example by Angela on how soda ash can naturally appear simply by the lye in her soap "meeting" the oxygen in the air around it.

Although soda ash can show up unexpectedly and present aesthetically-challenged soap bars, it can also lend itself to complementing colors and designs. There are easy ways to prevent it once you understand that water plays a large part. Most soapmakerss are busy and don't want to be presented with the task of removing soda ash on every batch made. Plastic wrap might be the easiest way to protect yourself against a surprise visit from the soda ash fairies!

What have you noticed about soda ash setting up on your soap?

Do you have any tips on removing or preventing it?

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