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Troubleshooting: Crackling & Glycerin Rivers in Soap

soap science and info
Glycerin Rivers in Indigo Soap

In the Modern Soapmaking Troubleshooting series, we explore various soap making problems and find out what went wrong plus share some tips and tricks to put the smack down on issues that pop up.

Today we're talking about...

Crackling and Glycerin Rivers in Soap

What is crackling and glycerin rivers in soap? The crackling effect found in some soaps is created by overheating or uneven cooling during saponification, as well as some colorants, and is often referred to as glycerin rivers.

Glycerin is a natural by-product of saponification, the chemical reaction that creates soap. Normally, the glycerin is dispersed throughout a bar, however, in the case of glycerin rivers, it collects together and creates this visual effect.

If the glycerin rivers are large enough, the soap will feel more pliable or softer in those areas.

What causes the problem? Glycerin rivers in soap is often caused by overheating/uneven cooling, and can be encouraged by certain colorants, like titanium dioxide (you may have heard of titanium dioxide crackles!).


These common soap making additives can increase your chances of seeing glycerin rivers:

  • Liquids with high sugars (milks, beers, fruit juices, etc.)
  • Pigments (oxides, ultramarines, etc.)
  • Fragrances that can cause overheating (florals, spices, etc.)

How do I prevent crackling? If crackling and glycerin rivers are common in your soaps, try to:

  • Ensure your colorants and additives are well mixed.
  • Reduce your soap making temperature, especially when using additives that tend to raise the overall temperature during saponification.
  • Elevate your soap mold to maintain a large amount of air flow to cool the soap down, or try using a soap mold that insulates less (wood molds insulate far more than other types.)


Is the soap usable? Crackling and glycerin rivers are an aesthetic problem, and do not affect the final soap's safety or use. If the glycerin rivers are large enough, it can cause the bar to wear down unevenly during usage.

Can the soap be fixed? Since crackling and glycerin rivers in soap are a visual problem, and not a functional issue, it is not necessary to fix.

However, if you want to attempt to fix the appearance, you can always rebatch! In most cases, it is not worth the effort!

Remember, soapmakers are always their own worst critics. Most (non-soapmaking) people think the effect is unique and cool!

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