We recently had a customer email us for help in getting her rosemary EO to “stick” in her CP soap. This is a common problem, as rosemary EO has a VERY low flashpoint of about 104 degrees. The flashpoint is the temperature at which the EO vaporizes – meaning that if you introduce it into an environment above that temperature, it is likely to vaporize. Since CP saponification happens at temperatures closer to 200 degrees, much of the rosemary EO will vaporize (i.e., just disappear!) if you attempt to make soap with the rosemary in it and put the whole thing through saponification.
So, what we advised the customer is to rebatch the EO into the soap. To do this, you make an unscented CP soap and let it saponify. You then shred, grate or cut up the soap as fine as possible, and place it in a double boiler or crockpot. Add some liquid – a nice, fatty liquid like whole milk or some cream is great, perhaps ice cold to prevent browning or scorching, and stir and cook on low heat.
Keep stirring and checking every few minutes until the soap is melted. Once the soap is starting to get soft, starting pushing it down with a potato masher. It will eventually start to fully integrate with the liquid, and start to get soft enough to add the EO – looking a bit like chunky mashed potatoes at this stage.
Now remove the soap from the heat (for instance, by taking the crock out of the metal part of the crockpot), and measure and stir until the soap is down as cool as possible – close to 100 degrees. When it gets that cool, stir in your EO, and put the soap immediately in the mold to harden.
Some people also like to add a dry clay with the EO to help anchor the scent. (The clay feels really good on the skin, too!) You can stir the EO into a tablespoon of kaolin or bentonite first and then stir the whole thing into your batch of soap before putting it into the mold.
Enjoy your rosemary soap!