There are several methods to incorporate the clay into your soap mixture. Since it's an inert substance, you can add it at any time during the process, as long as it gets mixed in completely. You can:
- Add it directly to the lye-water. You can add the clay directly to the lye water. This works best with lighter clays like kaolin. Sometimes the heavier clays won't dissolve well in the water and will tend to clump. There's also the danger of splashing the lye when you're mixing. This is my least favorite method.
- Add it directly to the oils.I think this method works best, especially if you're not using the clay as a colorant to do any sort of swirl. Once your oils have all melted, just add the clay directly to the melted oils. Use your stick blender to make sure that it is completely incorporated/dispersed. Look for clumps sitting on the bottom of the pot. Once the clay has all been dispersed in the oils, just add your lye-water and proceed as you normally would. This is the easiest method (and the method I used in these batches) but the clay is dispersed evenly throughout the whole batch for an even color.
- Make a slurry of oil and clay.This is the method you would want to use if you wanted a more variegated or mottled color in your soap, or to do a swirl. Once your oils have melted, add your lye-water solution. Just stir it gently until the lye and oils are lightly mixed together - don't mix too much! Ladle out a cup or two of the lightly mixed raw soap and put it into a large measuring cup or bowl. Add the clay and mix well. Mix the rest of the soap in the pot until it's almost time to pour. Then you can stir the colored reserve of soap back into the pot and make a swirl. Or you can pour the uncolored soap into the mold and layer or swirl the colored mix into it for an even more defined swirl. The challenge with this method is getting one large portion and one small portion of soap to trace at the same time - you need to work quickly.