Natural Colorant Rainbow Cold Process Soap

Learn how to create rainbow colored soap using only natural colorants, such as spirulina powder, indigo and madder root powder.

Learn how to create rainbow colored soap using only natural colorants, such as spirulina powder, indigo and madder root powder.

What You’ll Need:
Tall Narrow Wood Loaf Mold
44 oz. Basic Quick Mix
6.3 oz. Sodium Hydroxide Lye
14.5 oz. Distilled Water
2 oz. Lemongrass Essential Oil
1 oz. Lime Essential Oil
Natural Colorants Sampler Pack:
Madder Root Powder
Annatto Seeds
Indigo Powder
Spirulina Powder
Alkanet Root Powder

Learn how to create rainbow soap using only natural colorants, such as spirulina powder, indigo and madder root powder.

If you’ve never made Cold Process soap before, stop here! I highly recommend checking out our FREE four part series on Cold Process Soapmaking, especially the episode on lye safety. And if you’d rather do some reading, Bramble Berry carries a wide range of books on the topic, including my newest book, Soap Crafting. You can also checkout the digital downloads for that instant gratification factor.

SAFETY FIRST: Suit up for safe handling practices! That means goggles, gloves and long sleeves. Make sure kids, pets, and other distractions and tripping hazards are out of the house or don’t have access to your soaping space. Always soap in a well-ventilated area.

COLOR PREP:  Disperse 1 teaspoon of the alkanet root powder, spirulina powder and indigo powder into 1 tablespoon of lightweight liquid oil such as sunflower or sweet almond oil. Use a mini mixer to help get rid of any clumps. Then, disperse 2 teaspoons of madder root powder into 2 tablespoons lightweight liquid oil. In a separate heat safe container, add 1 teaspoon annatto seeds into 1 ounce liquid oil (I used sweet almond oil). Place the container in the microwave for about 20 seconds, or until the oil is warm to hot. Allow the mixture to thoroughly cool and the seeds to infuse the oil with a dark orange color. Strain out the seeds and set infused oil aside.

FRAGRANCE PREP: Measure 2 ounces of the lemongrass essential oil and 1 ounce lime essential oil in a glass, essential oil safe container. Set aside.

MOLD PREP: Line the Tall Narrow Wood Loaf Mold with freezer paper with the shiny side up. For tips on how to line the mold, click here.

ONE: Slowly and carefully add the lye to the water and gently stir until the lye has fully dissolved and the liquid is clear. Set aside to cool.

TWO: Fully melt the entire bag of Basic Quick Quick Mix until there is no cloudiness. Shake to mix and measure out 44 oz. Once the lye water and the oils have cooled to 130 degrees or below (and are ideally within 10 degrees of each other), add the lye water to the oils and stick blend until thin trace. If you’d like a harder bar of soap that releases faster from the mold, you can add sodium lactate to the cooled lye water. Use 1 teaspoon of sodium lactate per pound of oils in the recipe. For this recipe, you’d add about 2.5 teaspoons sodium lactate.



THREE: Once you’ve reached a thin trace, split the soap into six equal containers. Each container will contain about 300 mL.


FOUR: To each container, add the amount of dispersed colorants listed below. Use a whisk to thoroughly mix in the colorants.

  • Red: 1 Tbs. dispersed madder root powder
  • Orange: 2 tsp. dispersed madder root powder + 3/4 tsp. annatto seed infused oil
  • Yellow: 2 tsp. annatto seed infused oil
  • Green: 2 tsp. dispersed spirulina powder
  • Blue: 2 tsp. dispersed indigo powder
  • Purple: 1.5 tsp. dispersed alkanet root powder


FIVE: Add the essential oil blend evenly between the six containers, it’s okay to eyeball it. Use a whisk to thoroughly mix in the oil. If the soap is still extremely thin, give each color a few bursts with the stick blender to thicken slightly. The soap should be thin enough to pour and spread, but thick enough that it will support layers on top. Then, pour all the red colored soap into the mold. Tap the mold firmly on the counter to help even out the soap.


SIX: Carefully spoon the orange colored soap on top of the red, being careful to not let the orange soap break through the red layer below. Use a spoon to spread the orange soap evenly if necessary, then tap the mold firmly on the counter to help release any air bubbles. Continue layering the yellow, green, blue and purple soap into the mold, being careful to not break through to the layers below.


SEVEN: After you pour the purple soap on the very top, smooth the top with a spoon. Spritz the top with 99% isopropyl alcohol to prevent soda ash. Then, cover and insulate the soap for 24 hours. To help the colors pop, you want the soap to go through gel phase. If you’re soaping in a cold room, I would recommend placing the mold on a heating pad on medium heat for about an 30 minutes to help promote gel phase. After 2-3 days, remove from the mold and cut into bars. Allow to cure for 4-6 weeks and enjoy!


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