Coloring Water-Based Glycerin Soap

Question

I am making a water-based glycerin soap formula with very little oil. I tried using Iron Oxide Black (non-coated) to color it, but the color did not dissolve and was filtered out. What is the best way to color this type of soap base? Why did the Iron Oxide Black (non-coated) not work, and what color options are suitable? How can I prevent the color from fading?

MySkinRecipes Expert · Accepted Answer

Coloring Water-Based Glycerin Soap

Based on your formula being a water-based glycerin soap with very little oil, the issue you are experiencing with undissolved Iron Oxide Black (non-coated) is expected. Iron Oxides are pigments that do not dissolve in water and require proper dispersion in oil or a suitable agent.

For your type of soap base, water-soluble colors are the most suitable choice. They dissolve directly in the water phase, providing uniform color without undissolved particles. Examples include:

Black Color EasyWash™
Sorghum Red Water Soluble Color
Brilliant Blue‎ (CI42090) EasyWash™

There is also WaterMix™ Black, which is a water-based dispersion of Iron Oxide Black that might perform better than the powder in a water-based system, but testing is still recommended.

While water-soluble colors are easy to use, they can fade in alkaline environments like soap. To help protect the color from fading, you can add a UV protector such as Benzophenone-4.

Specific data on the alkali resistance of each color is generally not available. It is highly recommended to perform a small test batch with your chosen color in your soap formula to observe its stability over time.