Written by Elizabeth Mika
Founder and Maker, Bramble & Bear™ Soap Co.
About this Editorial: This article addresses a common question about soap in general. It is intended as general educational information and does not refer specifically to Bramble & Bear soaps.
A white, powdery or chalky coating can sometimes appear on the surface of cold-process soap. It is commonly called soda ash, and it is primarily made up of sodium carbonate.¹ Its appearance can be surprising, particularly if a white coating is mistaken for mold or spoilage. Soda ash, however, is a known phenomenon in cold-process soap and is generally a cosmetic surface issue rather than an indication that the soap has gone bad.²
How Does Soda Ash Form?
Soda ash can form on cold-process soap while saponification is still underway. Where fresh soap is exposed to carbon dioxide in the air, sodium carbonate can form and appear as a pale, powdery or chalk-like deposit on the bar.²
It is most noticeable on exposed surfaces. In my own soapmaking experience, small air pockets trapped in the batter can also create localized areas where soda ash appears along the sides or bottom of a bar.
Is Soda Ash the Same Thing as Mold?
Soda ash and mold are not the same thing. Soda ash is an inorganic mineral deposit—sodium carbonate—formed through a chemical reaction at the surface of the soap.¹ ² It typically appears dry and powdery or chalk-like rather than fuzzy or organic in appearance.
That distinction is useful because a pale coating on handmade soap can look unfamiliar to someone seeing soda ash for the first time. At the same time, appearance alone should not be used to identify every unusual mark on every bar. A change in color, odor, texture or overall condition may warrant a closer look rather than assuming automatically that it is soda ash.
Does Soda Ash Mean the Soap Is Defective?
Not necessarily. Soda ash can occur on properly formulated cold-process soap and is generally regarded as a cosmetic issue.² It may dull the surface, soften the appearance of colors or partially obscure a decorative design, which is why soapmakers often prefer to minimize it.
But the presence of ordinary surface soda ash does not by itself mean that the underlying bar has failed or will not perform normally.²
Why Does Soda Ash Form on Some Bars?
Soda ash does not develop in exactly the same way on every batch. Its formation can be influenced by factors such as exposure to air, temperature, water content and the stage of saponification at the exposed surface.²
As a result, one batch may develop little or no visible ash while another develops a more noticeable coating. The amount can also vary across the surface of the same loaf or bar.
Can Soapmakers Reduce Soda Ash?
Yes, although it cannot always be eliminated completely. Soapmakers use several methods to reduce its formation, including limiting exposure of freshly poured soap to air, managing processing conditions and applying isopropyl alcohol to the surface shortly after pouring.² Even with those measures, some soda ash can still appear.
Can Soda Ash Be Removed?
Often, yes. One common finishing method is steaming the surface of the cured soap, which can reduce or remove the powdery appearance.² Soapmakers may choose to do this simply because the finished bar looks cleaner and its colors or design are easier to see.
The treatment is cosmetic rather than a repair to the underlying soap.
Why Does This Matter to Buyers?
Because appearance can easily be mistaken for condition. A customer seeing an unfamiliar white coating may reasonably wonder whether a handmade bar has spoiled, developed mold or been made incorrectly.
Knowing what soda ash looks like provides useful context: a dry, powdery coating on cold-process soap can be a normal result of the chemistry taking place at the soap’s surface.
The Bottom Line
Soda ash is primarily sodium carbonate that can form on cold-process soap when the fresh soap surface is exposed to carbon dioxide in the air during the early stages of saponification.¹ ² It is different from mold and, when it is ordinary surface soda ash, is generally a cosmetic issue rather than evidence that the soap is defective.²
Soapmakers can take steps to reduce or remove it, but it is one of the visual characteristics that can occasionally appear in traditionally made cold-process soap.
Related reading
- Once You Know, You Know: Is It Really Soap? →
- Soap, Cosmetic, or Drug? What Does the Label Really Tell You? →
Sources
¹ U.S. Environmental Protection Agency, “AP-42, Chapter 8.12: Sodium Carbonate.” Sodium carbonate (Na₂CO₃), commonly known as soda ash, is an inorganic salt used in products including soaps, detergents, chemicals and glass.
² Soap Queen / Bramble Berry, “Explaining and Preventing Soda Ash.” The technical guidance describes soda ash on cold-process soap as sodium carbonate formed when sodium hydroxide near the soap surface reacts with carbon dioxide in the air. It also discusses factors associated with its formation and methods used to reduce or remove it.
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