White Spots on Soap: Soda Ash, Stearic Spots, or Something Else?

You cut a beautiful batch of handmade soap, take a look at the bars, and…what are those white spots? Is this soda ash?
Sometimes it is. But sometimes it’s not.

White spots, speckles, patches, streaks, and coatings can have several different causes, and unfortunately, a photo alone doesn’t always give us enough information to identify which one you’re looking at. Your recipe, temperatures, water content, additives, and whether the soap gelled can all provide important clues.

So before we diagnose every mysterious white thing as soda ash, let’s look at some of the possibilities.

First: What Does Soda Ash Look Like?

Soda ash is probably the best-known white stuff that appears on cold-process soap. It usually looks like a powdery, chalky, or sometimes slightly crystalline coating on the surface of the soap.

It forms when sodium hydroxide interacts with carbon dioxide in the air, creating sodium carbonate. You’ll most commonly see it on surfaces that were exposed to air, particularly the top of a loaf or the outside surfaces of freshly cut bars.

Soda ash can be very light and barely noticeable, or it can cover a substantial portion of the soap. It can also form some surprisingly interesting patterns, which is one reason identifying it from a photograph isn’t always as easy as you might think.

The good news is that soda ash is generally a cosmetic issue. It doesn’t mean you’ve ruined your soap.

I’ve experimented quite a bit with soda ash, including different ways to encourage, prevent, and remove it. If what you’re seeing looks like a surface coating rather than spots within the bar itself, take a look at my guide to controlling soda ash on handmade soap. It includes 12 different examples, which can be particularly helpful when you’re trying to compare your soap to the real thing.

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What Are Stearic Spots in Soap?

If the white areas appear inside the soap rather than simply sitting on its surface, we need to start looking at other possibilities.

One of them is commonly called stearic spots.

The fats and oils we use for soapmaking are made up of different fatty acids. Hard fats and butters tend to contain larger amounts of saturated fatty acids, including stearic and palmitic acids. These fatty acids have higher melting points than many of the other fatty acids in our soapmaking oils.

That matters when we make soap.

If your melted oils begin cooling enough for some of those higher-melting components to start solidifying before or during mixing, they may not remain evenly distributed throughout the soap batter. The result can be lighter, waxy-looking speckles, spots, or patches in the finished soap.

You’ll sometimes hear this phenomenon described as fat bloom, particularly when talking about fats such as cocoa butter. The general idea is similar: fats can crystallize into structures that become visible. In soapmaking, however, stearic spots or stearic/palmitic spots are more useful terms because they describe what soapmakers are usually seeing.

This is one reason your oil selection and soaping temperature matter when troubleshooting white spots. If I know that your recipe contains a substantial amount of cocoa butter, shea butter, palm oil, tallow, or another hard fat, that gives me a very different clue than if you’re making a 100% olive oil soap.

Suspected stearic/palmitic spots.

White speckling like this can be associated with higher-melting fatty acids, but appearance alone isn’t enough to confirm the cause. These particular batches had several other possible variables, making them a great example of why detailed batch records are so important when troubleshooting soap.

This is a perfect example of why troubleshooting starts long before something goes wrong. When you document your ingredients, fatty acid profile, temperatures, water, additives, gel phase, and process for every batch, you have something concrete to compare when one batch behaves differently from another.

Photos courtesy of Soapy Friend V.P.

Can Soaping Too Cool Cause White Spots?

It can, particularly when your recipe contains fats with higher melting points.

This doesn’t mean there is one magic soapmaking temperature that everyone should use. I am a big believer in understanding why we’re choosing our temperatures rather than memorizing rules such as “always soap at 100°F.”

Instead, think about what is in your particular recipe.

You want your hard fats completely melted and your combined oils warm enough that those fats remain melted while you’re working. If your oils become cloudy or begin developing visible solids while you’re preparing your batch, that’s a pretty good clue that something is beginning to crystallize.

Your recipe determines what “too cool” means.

This is also why knowing only that someone “soaped at room temperature” doesn’t necessarily tell me enough. Room temperature could be 68°F in one soapmaker’s house and 82°F in another, and two recipes sitting at exactly the same temperature can behave differently because they’re made with completely different fats.

Air Bubbles Can Look Like White Spots, Too

Sometimes the explanation is considerably less exciting: you’re looking at tiny air pockets.

Small bubbles incorporated into soap batter can appear as pale or white dots after the soap is cut. Depending on the size of the bubbles and the color of the soap surrounding them, they can look remarkably similar to spots caused by an ingredient.

Look closely at the spots. If they appear to be tiny holes or little round cavities rather than solid white material, trapped air becomes a much more likely explanation.

Air can be introduced while stick blending, stirring, or pouring. Tapping your filled mold against the work surface can help release larger trapped bubbles before the soap sets.

Could White Spots Be Undissolved Lye?

This is the possibility we don’t want to casually diagnose from a photograph.

White material inside soap can sometimes indicate a more significant formulation or mixing problem, including pockets containing excess alkali. That’s why I don’t recommend telling someone that mysterious white spots are definitely harmless based solely on how they look.

Think about the entire batch.

Was the sodium hydroxide completely dissolved before you added the lye solution to your oils? Did anything unusual happen while you were mixing? Did the batter separate? Was the recipe run through a reliable soap calculator? Are there liquid-filled pockets or other unusual areas in the bars?

If there is a genuine possibility that the soap contains concentrated lye, don’t use or sell the soap until you’ve figured out what happened. A zap test can help determine whether your soap contains excess unreacted lye, but it needs to be performed correctly. If you’ve never done one before, here’s my guide to how to safely perform the zap test.

This is also an excellent example of why troubleshooting requires more than a picture.

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What About Additives?

This is where the detective work gets interesting.

Colorants, clays, salts, sugars, fragrance oils, essential oils, milks, botanical ingredients, and other additives can all affect what happens in a batch. Some can clump if they aren’t dispersed thoroughly. Some affect temperature or trace. Some can change the appearance of the soap as it saponifies or cures.

Even fragrance can matter. If someone tells me, “The only things I added were oils, color, and fragrance,” I still want to know which oils, which colorant, and which fragrance.

In soapmaking, “nothing unusual” can turn out to be the most useful clue in the entire recipe.

Partial Gel Can Create Light and Dark Areas

Sometimes what looks like a mysterious discoloration isn’t a deposit or spot at all. It is a difference in the soap itself.

Cold-process soap that goes through gel phase often develops a somewhat different color and appearance from soap that doesn’t gel. If only part of a loaf gets hot enough to gel, you can end up with a darker or more translucent-looking area surrounded by lighter soap.

The classic partial-gel pattern tends to appear toward the center of a loaf because the center retains more heat. It doesn’t generally create tiny individual white speckles, but larger light and dark areas can easily make a soapmaker wonder whether something went wrong.

If you’re seeing a darker ring, circle, or oval in the center of your bars, take a look at my guide to partial gel in cold-process soap. It includes examples of what partial gel looks like, why it happens, how to prevent it, and even how you may be able to fix it after cutting.

Again, knowing whether you encouraged gel, prevented gel, or simply left the mold alone gives us another useful piece of the troubleshooting puzzle.

So, How Do I Know What’s Causing the White Spots on My Soap?

Instead of beginning with the appearance of the spots alone, look at where they are and how they behave.

A powdery or crystalline coating primarily on the exposed surfaces points us toward soda ash. Solid-looking pale spots distributed through a soap made with hard fats may point us toward stearic or palmitic crystallization. Tiny cavities may simply be air bubbles. A large lighter area surrounded by darker soap may be related to partial gel. Unusual pockets, separation, or suspicious material within the bar deserves more investigation before deciding the soap is safe to use.

And sometimes the correct answer is simply: we need more information.

Soapmaking is chemistry, and your finished bar is the result of an entire process. Two bars with very similar-looking white spots may have developed them for completely different reasons.

That’s why one of the first things I ask when someone shows me a troublesome batch is, “What’s your recipe?”

Not because I’m trying to steal your secret formula. I promise. 😂

I’m trying to understand what happened.

The Most Important Thing: Don’t Diagnose Soap by Photo Alone

Photos are incredibly helpful. They’re just one part of the story.

When someone posts a picture of a soap with white spots, I can look at the shape, location, texture, and distribution and say, “Hmm, that looks more like stearic spots than soda ash.”

But that’s a starting point, not necessarily the final answer.

Tell me what oils you used. Tell me how much water was in the recipe. Tell me your superfat, temperatures, additives, method, and what happened with gel. Those details allow us to move from “Here’s what it looks like” toward “Here’s what probably happened and why.”

And understanding the why is the really useful part, because then you know what you might want to change the next time you make soap.

Continue Learning with Soapy Friends

One strange batch can teach you an incredible amount about soapmaking. Once you start connecting what you see in the finished bar with your ingredients, temperatures, water, and process, troubleshooting becomes much less mysterious.

If you’d like to continue learning and soaping along with me, here are a few great next steps:

Controlling Soda Ash on Handmade Soap is the place to go next if your white spots really do look like soda ash. I’ve included 12 examples so you can see just how differently soda ash can appear.

Cold Process Soap Troubleshooting Guide covers more of the common surprises you may encounter when a batch doesn’t behave quite the way you expected.

The Soap Maker’s Batch Journal helps you keep the recipe and process information you’ll need when it’s time to figure out what happened — or recreate a batch that turned out absolutely beautifully.

And if you’d like ongoing classes, experiments, and soapmaking help, you can join me inside the Soapy Friends membership.