The Experiments: Charcoal Swirl CP Soap

In this post I talk about why and how I made my cold process charcoal swirl soap. I start with a little bit of science and then dive into the recipe (as percentages) and instructions/steps. I have an exact recipe for a 45 oz batch of soap here.

On Monday I decided to try my hand at the swirl design technique in some cold process soap, and settled on using activated charcoal, which I knew would produce a beautiful contrast with the base soap mixture. Activated charcoal itself is a great additive for cosmetic products not only for its color, but also for is potential ability to capture carbon-based impurities.

The science:

Labmuffin Beauty Science has a great post summarizing the science behind how carbon works to capture other carbon-based molecules. The basic idea is that the surface of activated charcoal is extremely porous, giving it lots of room to capture and hold on to dirt, oil, and other carbon-based things. Labmuffin Beauty Science also points out that carbon is very effective when ingested, but that the jury’s still out on whether it is as effective in topical applications. Either way, it may work (some companies, such as Biore, claim that it definitely does), and there’s no harm in adding it!

The following pictures are from the gorgeous resulting soap:

The Recipe (%)

I used five different oils and fats in this recipe to produce a nice, cleansing, and conditioning bar of soap.

Extra Virgin Olive Oil35
Coconut Oil (92°)30
Shea Butter (Unrefined)15.5
Cocoa/Cacao Butter (Unrefined)14.5
Castor Oil5

As with my other soap recipes, I use SoapCalc to determine the amount of Lye and Water that I need.

SoapCalc Option%
Water as % of Oils38

Finally, I chose to add 1 Tbsp of activated charcoal to my recipe, which worked out to be 1.25% of the weight of oils in my batch size. I chose not to add any essential oils this time, so that the natural scent of the unrefined cocoa butter could dominate. This recipe would certainly work just as well using refined butters, but the natural scent of the cocoa butter will not be there.

Other Ingredients%
Distilled Water*
Activated Charcoal1.25%

*Will depend on the SoapCalc Superfat and Water as % of Oils percentages that are set.I

On my recipes page, I’ve included exact ingredient amounts for a batch size of 45 oz.


  • Safety gear: eye protection, a ventilator mask that is suitable for fumes produced from the lye mixtures, gloves to prevent lye burns, long sleeves, and close-toed shoes
  • A well-ventilated place to work in, free from children and small (or large) animals
  • A double boiler
  • An immersion blender
  • A spatula (preferably two, one to work with the charcoal soap mixture, and one to work with the non-charcoal soap mixture)
  • Several large bowls; one for the main soap mixture, and one for an ice bath that can fit a heat-proof bowl into it. The heat-proof bowl is for mixing the water-lye solution
  • A non-reactive (plastic or wooden) spoon for mixing the water-lye solution
  • Two scales, one that can handle larger weights for measuring out oils/fats, and a smaller, precise scale that can measure out the lye (to 0.01 g)
  • Several measuring cups; at least one with a handle for measuring and pouring the lye, and one larger one with a handle for mixing and pouring the charcoal soap mixture
  • Optional:
  • A thermometer
  • A gear tie for swirling
  • Equipment for cutting the soap; this can be as simple as a sharp knife and cutting board!

Step-by-Step Instructions

I. Prepare your oils/fats:

  1. Measure out butters and solid oils and place in double boiler over low heat to melt.
My double boiler setup.

2. Measure out and combine the liquid oils in large container that will be used to combine with lye solution. Reserve some liquid oils to later saturate with your activated charcoal (this makes it easier to mix the charcoal with the soap). Place in a container that is large enough and sturdy enough to place your immersion blender into. This will be used to mix the charcoal with some of the soap mixture.

3. Measure out the charcoal powder and combine well with the reserved oil and set aside.

4. Wait until butters and solid oils are fully melted before moving on.

5. Once fully melted, add melted butters/oils to liquid oils in the main container. Aim to work between 90-130° F (this can affect how quickly your mixture traces/gels).

II. Prepare your water-lye mixture:

6. Prepare an ice bath in a large bowl, and place heat-proof glass mixing bowl inside (this will be used to mix the water-lye solution).

The prepared ice batch for the water-lye mixture.

7. Add the (measured-out) distilled water to the heat-proof glass mixing bowl.

8. Put on your safety gear and turn on ventilation. Measure out lye into a separate container with handle.

9. Slowly pour the lye into the distilled water, mixing with your long, non-reactive spoon as adding.

III. Combine the lye water with the oils/fats:

10. Once finished combining the water and lye, check the temperature. If it is too hot, give it some time to cool to the range above, and then add to the main container with oils.

11. Take a spatula and initially mix together the oils and water-lye solution. Then, use your immersion blender to mix lye and oil until light trace.

Bringing the mixture to light trace.

12. Pour some of the mixture into the container with the oil-charcoal mixture. Use a spatula to scrape down the sides and gently mix together. Further mix with your immersion blender.

Mixing the charcoal soap.

IV. Place the mixture into your mold(s) & decorate:

13. Add the mixtures into a rectangular soap mold in layers. I layered mine: 1. mixture without charcoal, 2. mixture with charcoal, 1. mixture without. I also reserved some charcoal mixture for the top.

14. At this point, I used a gear tie to swirl the mixture. I pushed the gear tie down to the bottom, a centimeter or two from one side, moved over to the same distance from the other side, and brought the gear tie almost all the way up again, and back to swirl again. I did this several times.

The gear tie inside of the rectangular/loaf mold.

15. Finally, I placed the remaining charcoal mixture on top for decorating!

Decoration on top of loaf.

V. Cut & cure your soap:

16. I cut the soap after 24 hours, and stored it to cure for 4-6 weeks.

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