The River Runs Deep: An explanation of glycerin rivers

Soapmaking is as much a science as it is an art. Countless variables can affect the look and feel of your soap. Temperature is a huge factor in soapmaking, and today we’re tackling a phenomenon that occurs when soap gets too hot.

An extreme example of soap “cracking,” also known as glycerin rivers.

Known as soap “cracking” or glycerin rivers, the phenomenon above occurs in cold process soap. The little rivers aren’t harmful. Gycerin is a naturally occurring by-product of the soapmaking process.

Glycerin is a humectant, meaning it attracts and retains moisture. It’s also a natural solvent, which gives it great cleaning power. In short, glycerin is one of the things that makes handmade soap so amazing. However, when cold process soap gets too hot the glycerin can congeal, becoming more apparent and visible, forming the “rivers”. When glycerin rivers are thick or clustered in one section of soap, that area of soap may be softer than the rest of the soap. Glycerin rivers are more likely to be seen when oxide colorants are used, particularly Titanium Dioxide. Oxides are dense, opaque colors and are more likely to show rivers than more translucent micas or transparent liquid colorants. Here is an example of glycerin rivers in soap colored with titanium dioxide:

There are glycerin rivers all throughout this soap, but the red circles indicate where it’s particularly clustered. The good news is glycerin rivers are purely cosmetic and not harmful to your soap. They may not be what you’re going for, but in all likelihood you’ll be the only one to notice!

We use Titanium Dioxide and other oxides all the time in the Soap Queen Lab, and there is no need to stray away from them. Glycerin rivers are somewhat uncommon, but there are a few ways to lessen the chance that glycerin rivers will appear in your soap. They include:

  • Mixing your colorants well, particularly if you use an oxide and especially if you use Titanium Dioxide. We recommend dispersing 1 teaspoon of colorant in 1 tablespoon of light liquid oil and then stirring with a mini mixer. We also have a SQTV Short on prepping colorants for cold process soapmaking for more in depth information:

  • Low temperatures are your friend! If you are getting glycerin rivers, lower your temperatures. If lowering the temperatures of both your lye water and oils by 10 degrees doesn’t do the trick, you can use room temperature lye water and oils heated to around 100 degrees F to lessen the chance of rivers. Then, consider popping the soap in the freezer or running a fan over it to keep it cool and prevent gel phase.
  • Reducing the amount of water in your recipe can also help prevent glycerin rivers, this is called water discounting your soap.
  • Be conscious of the fragrance or essential oil you choose too. Some oils will heat the soap no matter what you do, so be careful to choose a fragrance oil that behaves well in cold process.

Even with all these tips, there may be a few batches where you’ll see glycerin rivers. However, that doesn’t have to be a bad thing! Sometimes the rivers can add charm and character to your soaps.

If you have any additional tips and tricks for preventing glycerin rivers, I’d love to hear them. Post them below.

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29 Comments

  1. Shelia says

    Thank you, You never fail me. I made a batch of Cold Water fragranced soap over the weekend. Used TD and Ultramarine Blue in a drop swirl. After I cut the bars, I noticed that some of the portions of the white had turned clearish. It’s nowhere near as bad as your examples. Glad to know what it is. Mine look pretty good…like it was intentional. Thanks for the info, you saved me a lot of internet searching.

  2. BB says

    I always seem to get glycerin rivers in my Beeswax soaps. Any tips on how to prevent that since I have to keep the temp up to prevent the beeswax from solidifying before I get it mixed in?

  3. Vicki says

    I was having this phenomenom occur quite often when I started out and was using homemade wood molds and insulating with two towels. Turns out this was overkill and the wood alone is enough insulation to get to gel phase. Just as a precaution though, when using certain fragrances now, especially with titanium dioxide, I soap at cool temps and sometimes freeze after pouring.

    • says

      Hi Nancy!

      While glycerin rivers are often an effect people try to avoid, I agree, it can look really cool! If you are wanting to achieve glycerin rivers in your soap, I would recommend soaping hot and using Titanium Dioxide! :)

      -Amanda

  4. Laura Luciani says

    I had this happen in one of my “masculine” soaps, which was okay because it gave it a “leathery” look. But thank you for the explanation. I had been curious as to what caused the rivers. As always, Soap Queen is a wealth of information.:-)

  5. Patricia says

    Thank you for this post, you guys always provide the best education in CP soap you can find online. I get glycerin rivers very often and I love it! I think it actually adds character to my marbling effects and usually post pictures for my customers on Instagram, emphasizing the -good for your skin- glycerin content.

    • says

      Hi Patricia!

      I’m so glad you found this post helpful! We are always happy to share as much information with soapers as possible :) I agree, I think glycerin rivers can look really cool, and do give a great visual to customers!

      -Amanda with Bramble Berry

  6. says

    I too think it’s an interesting look! I have also seen a little bit of these “rivers” in the old oil paintings that are in the museums in Europe…probably because they used titanium dioxide as one of their paint pigments? Thank you for the great post!

  7. Irina says

    Thanks for the explanation! I got those rivers in one of my latest soaps and I was really surprised, never seen them before. Also, the soap was too soft and it took a week to get it out of the mold. But when it was out and hardened, it turned out just fine. I tried to dilute the colorants in glycerin, so it was just natural that the rivers appeared :)

    • says

      Hi Irina!

      I’m glad that you found this blog post helpful :) I’m glad to hear that your soap hardened up, some batches can take a little bit longer than others! That does make sense, I’m glad we could help you figure out what happened :)

      -Amanda with Bramble Berry

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