There are three tests for natural colorants:
- A lye test
- An oil test
- A final test in a small batch of soap
The Lye Test
To test how your colorant will react to the lye, dissolve about a tablespoon of lye into a half cup of water. Stir until the lye is completely dissolved and let it cool. Slowly add some of the plant material. You dont need to use much perhaps ¼ teaspoon of powdered colorant, or a few leaves of a fresh. TAKE NOTES!! In your notebook, jot down the amount of plant material used, and what color it turned. Check the solution again in a few hours. Then let it sit for about 24 hours and check again.
The Oil Test
Heat up about 4 ounces of oil. (I prefer to use coconut oil or lard so that I know that the oil is not imparting any color to the final results.) Add your colorant as before, and let it steep. Check back in a few hours and again after about 24. Again, TAKE NOTES!!
The Soap Test
After youve tested the colorant in both the lye and oil, you should be ready to try it in a small batch of soap. Depending on whether the colorant acted better in the lye or the oil will determine when you add it to the mix. Some plant materials work better when steeped in the lye solution, others work better when added at trace.
Unfortunately there is no hard and fast rule for how much of each colorant to add to your soap. Different plants have stronger coloring abilities, as well as each person's tastes are different. When Im testing out a recipe, I usually start with 1 tsp. of colorant for each pound of oils in my recipe. Then, based on those results, Ill adjust the amount from there. If you're going to steep the colorant in the lye water, mix your lye-water first, then add the color. Let it steep for a few minutes - or a few hours if necessary. Then using this colored lye-water, make your soap.
If you're going to add the color to the oil, you can either add it at the beginning to the oils, or at the end, at trace. Either way seems to work about the same. As before, TAKE NOTES - how much of the colorant you used, when you added it, how it reacted in the soap. Your memory may be good now, but several months from now, when you want to duplicate your wonderful results, you'll be grateful for those notes.