What Causes a White Film on Handmade Soap?

Learn what causes a white film on handmade soap, how you can prevent it, and if a soap with white film is safe to use.

You’ve made the most beautiful cold process soap, complete with killer swirls and an amazing scent. You can’t wait to take it out of the mold, cut it into bars, and admire your handiwork.

After letting it set a day or two, you’re disappointed to see that your beautiful soap is not quite so beautiful anymore. The soap bars have a layer of white film across the surface, effectively covering up your lovely swirl job.

What the heck is that white film on handmade soap? And what can you do about it?

What Is The White Film On Handmade Soap?

That weird, white film on cold process soap that develops on the surface of the bars is called soda ash. It generally appears during the first few days after making your soap, either while it’s setting in the mold or just after you’ve cut and during cure.

Soda ash happens to nearly every cold process soap maker at some point in time.

Soda Ash Is Harmless

The good news is soda ash doesn’t affect the safety of your soap or how your soap works. It’s completely harmless. It may be ugly as heck, but harmless.

Soap with soda ash is perfectly safe to use.

In fact, the white film on handmade soap will wash away during the first use or two.

What Causes Soda Ash On Soap?

There are a few different reasons why soda ash, or a white film on handmade soap, appears.

Exposure to Air

The consensus is that soda ash is sodium carbonate, which forms when lye reacts to carbon dioxide in the air during saponification. This explains why soda ash only appears on the surface of your soap bar, or any edges exposed to air, and never in the middle of the bar.

(If you have white streaks in the middle of your soap bars, they are a different sort of problem; most likely glycerin rivers.)

In a perfect world, if you protect the surface of your soap from air during the entire time of saponification it should technically prevent soda ash. But, this isn’t always the case.

There are other factors that contribute to soda ash development.

Soaping At Cool Temperatures

The funky thing about soda ash though, and the reason it plagues soap makers so, is it’s so sneaky. You can make a batch of soap that turns out perfectly, but make the same recipe in the same way a few weeks later and it will ash.

In my experience, temperature plays a role in soda ash development.

Soaping at cooler temperatures (under 85 degrees) seems to trigger it. So do big fluctuations in temps during the saponification process.

For example, you may have more problems with soda ash during the winter and very rarely in the warm summer months.

Pouring at Thin vs. Thick Trace

Soap that is poured at very thin trace seems to develop soda ash more than soap that is poured at a thicker trace.

I hypothesize that soap poured at a thicker trace can generate more heat, making temps more stable after the soap batter has been poured into the mold versus soap poured at thin trace. Gelling the soap seems to prevent ashing.

Some fragrance oils trigger soda ash, but this is probably the least common trigger.

How To Prevent Soda Ash on Soap

Although soda ash may still pop up every now and again (it is sneaky after all!) there are a few things you can do to prevent it. Experiment with a few of these and see what works best for you.

Soap at Warm Temperatures

Try mixing your lye water and oils together when they’re both between 110 to 120 degrees.

If you make milk soap, though, you don’t want your mixture that hot. Instead, blend at about 90 to 95 degrees. This works for me, but you’ll want to experiment with your recipe.

Keep the Soap Warm Throughout Saponification

Keep your soap nice and warm during the saponification process. Insulate your soap mold well with a few towels or a thick blanket, especially during the wintertime.

Pour at a Medium to Thick Trace

You’re looking for thick gravy to nearly pudding consistency. This really makes a HUGE difference for me!

Protect the Soap From Air

Put a lid on your mold before you insulate. My “lid” is just a thick piece of plywood I place over my mold. Make sure the lid isn’t touching the soap’s surface, though.

In cooler weather, or in soap recipes that I’ve had problems with ashing before, I leave the soap in the mold for at least three entire days, and often more than a week, before uncovering.

The batches I rush and open the lid earlier come out of the mold beautifully only to develop ash hours later. Again, this happens mostly in the winter months so I speculate it’s a temperature fluctuation thing.

Soap At a Water Discount

This is probably the MOST helpful thing I do to prevent soda ash. Soap batches that use full water seem to have more issues with soda ash than those with less water.

Are you totally confused about what I mean when I say ‘full water’ and ‘water discount?’ That’s OK, I had trouble with this concept when I was a new-ish soaper too!

Unlike oil and lye amounts within a soap recipe, the water amount needed is a range. You can use a bit less or more water in any given recipe and everything will still come together perfectly. (Mind blown, right?)

This is because water is only needed to dissolve the lye–the water amount plays no part in saponification.

Using full water means you are using 3 parts water to 1 part lye, making a 25% lye solution. Recipes that use full water are more prone to developing soda ash.

Reducing the amount of water in a recipe means you are working at a water discount. This could mean using 2 parts water to 1 part lye, making a 33% lye solution. Or using 1.5 parts water to 1 part lye, making a 40% lye solution. (Just a side note, you never want to use less water than lye, as your lye will not dissolve properly.)

I’ve found using a 38% to 40% lye solution works best for reducing soda ash. But you can play around with the water amount that works best for you.

And, if your head is spinning trying to figure this all out, I have an entire lesson about water discounts and how to create a specific strength lye solution in my online Soap Formulating Course.

Things That Don’t Work to Prevent Soda Ash (In My Experience)

These soda ash fixes are commonly recommended and, while they may work for other soap makers, they were big duds for me. I DON’T recommend:

Spraying the surface of the soap with rubbing alcohol right after pouring. This never made a lick of difference, in my experience.

Covering the surface with plastic wrap. Yeah… no. It’s incredibly messy and ruins the pretty surface of the soap.

Adding a touch of beeswax to the recipe. I never had a worse case of soda ash as in the soap I made with beeswax.

How To Remove Soda Ash From Soap Bars

Even with careful soaping, there will be times that your bars ash. If it hasn’t happened to you yet, it will one day.

Since soda ash is purely cosmetic, you can use those bars as-is, ash and all. You won’t notice a difference.

But there are a few things you can do to remove ash from your bars and get them looking all pretty again.

My go-to treatment: Spray the soap with alcohol until the surface is visibly wet. Yes, here is where spraying with rubbing alcohol can help! After spraying, let dry. You may need to do this more than once in severe cases of ash, but it works incredibly well.

I’ve also had good results with steaming the ash away. Quickly run the ash-ridden surface through the steam from a tea kettle. Be careful you don’t burn yourself, though.

If you have a soap planer, you can also shave the affected areas off. This will give you a bit of waste. Also, if you have a beautiful textured top that you’ve worked to get just right, planing it off isn’t a great option.

Embrace the Ash!

Instead of getting bummed over soda ash, learn to embrace it. I used to hate soda ash, but my perception is changing.

This change of heart came after I saw a soap maker at a craft fair who used soda ash to her advantage, creating the loveliest soft purple bars with textured and ashed tops that were To. Die. For.

It made me look at soda ash in a different way. Although I don’t always love it, I can appreciate it as part of the charm of handcrafted soap.

If your soap has ashed, try to enjoy the rustic beauty of your bars even if they didn’t turn out exactly like you envisioned.

Because you made soap….

And that’s pretty awesome, ash and all.

So, do you want to learn more about formulating your own soap recipes?

Check out The Soap Formulating Course and learn how to create your own custom soap recipes with my easy step-by-step method. You can stop following other people’s soap recipe and start making your own!

Want to get an insider’s look at what the course is all about? Get complimentary access to the first module!