How to Use Indigo to Color Cold Process Soap

If you’ve ever tried to use indigo to color your cold process soap and ended up with a nasty gray – or worse yet, no color at all – this post is for you! I’ve been there too, which is what drove me to figure out the best ways to get a beautiful color – from a light grayish blue to beautiful teal to dark navy blue. But what about color transfer and colored lather? Can you use too much? Definitely!

It should be noted that there are different types and intensities of indigo available from different suppliers and they are used in different ways. I will show you the benefits and disadvantages of each.

Let’s start with the different types. There are two different types of indigo: powdered and pre-reduced crystals. You can purchase the powdered form from several reputable soap supply vendors. (Thanks to the samples provided by Amanda Gail of Lovin Soap, I tested powders from Bramble Berry and From Nature With Love.) The only supplier of the crystals that I could find is Dharma Trading.

There are also different intensities of indigo powder. In addition to the powders from Bramble Berry and From Nature With Love, I tested a powder from Botanical Colors. They are not a soap supplier, but market their products to those who dye fabrics. It is an organic indigo powder that is much more saturated than the ones I tested from the soap suppliers.

I experimented with four different ways of incorporating indigo in cold process soap. 1. adding it to the hot lye solution, 2. creating strong oil infusions and adding after the soap was mixed, 3. dissolving the crystals in hot water, allowing it to cool and adding it after the soap was mixed, and 4. incorporating an oil infusion in addition to soap that already had indigo added to the lye solution. The powdered indigo can be added either to the lye solution OR in an oil infusion, but the pre-reduced crystals must be dissolved in hot water.

It’s important to use a soap recipe with light colored oils so that it doesn’t yellow and turn what could have been a lovely blue soap into an icky green or brown. I also made sure every batch went through gel stage to brighten/darken the colors. In a couple cases, the soap only reached a partial gel. This is the recipe I chose for all of my testing:

33% tallow
33% avocado
30% coconut
4% castor
5% superfat
30% lye concentration

Experiment #1: Testing saturation levels with the organic indigo from Botanical Colors using oil infusions.

Lightest layer: 1/16 tsp indigo in 1 tsp oil in just under 1 c soap; middle layer: 1/8 tsp indigo in 1 tsp oil in just under 1 c soap; darkest layer: 1/4 tsp indigo in 1 tsp oil in just under 1 c soap

The colors are grayish blue, just as they should be! I was worried that the darkest layer might bleed, so I did some testing on a cream-colored wash cloth:

Just the slightest bit of color transfer onto the wash cloth

I love that you can treat this indigo just like mica by pre-mixing it with a bit of oil and adding it to portions of soap. It makes it easy to do design work. However, the indigo takes a bit longer to incorporate than mica, so it requires you to plan ahead at least a few hours before you want to make the soap.

Experiment #2: Testing organic indigo and pre-reduced indigo crystals in the lye solution.

I used 1/2 tsp of indigo in both lye solutions for the same size batch (16 oz of oils). The powdered organic indigo is pictured on the left, and the pre-reduced crystals are on the right in the following photos:

Both types of indigo resisted being incorporated into the hot lye solution – the powdered even more than the crystals. The crystals turned green and also produced a rank odor when added to the lye.

By this time, the lye solution is starting to cool, but the indigo is still resisting in both solutions. I even considered that I might have to toss the one with the powdered organic indigo at this point.

This is how both solutions looked right before I added them to the oils. The organic powder finally incorporated – mostly. The crystals formed a skin on top and the solution remained a rather bright green.

This is the particulate that remained in the bottom of the measuring cup after I poured out the lye solutions.

The results of this test are rather stunning! The organic indigo remained a very dark blue – even darker than the darkest layer of the oil infused soap, while using almost half the amount.

Organic indigo from Botanical Colors in final soaps

This begs the question whether the lather of this super dark blue soap would stain the cream-colored washcloth:

This dark color definitely colored the washcloth, but fortunately it washed out! I probably still wouldn’t sell a soap colored this dark.

The soap colored with the crystals also came out beautifully – a very lovely dark greenish blue, with a lighter teal green around the outside. I think this may have happened because I put this soap in the oven to force gel stage and the heat pushed the green plant material to the outside. Just a theory though.

Soap colored with pre-reduced indigo crystals

And the color bleed test:

This one transferred just slightly more color than the darkest layer of the BC infusion soap, but not as much as the BC lye solution soap. The indigo washed out of the cloth, but I would still consider using a bit less.

The advantage to using this method is the ability to use much less colorant to get a strong color. The disadvantage is that you can’t do any design work. Your soap will be all one color – all one very lovely color though! I would also advise mixing the lye solution in a stainless steel container instead of plastic, as the indigo has now permanently stained the plastic measuring cups.

Experiment #3: Testing indigo powders from Bramble Berry and From Nature With Love using oil infusions.

I could tell just by looking at the color of the powders from these two different suppliers that the results from this experiment would be different.

Indigo powders

For this batch, I made 4 cups of soap (24 oz. of oils). Each oil infusion was made with 1 teaspoon of avocado oil mixed with the following amounts of indigo powder:

The intensity of the color is quite different between these two different suppliers! You can also observe the color difference between the gelled and ungelled portions of the soap.

Experiment #4: Testing pre-reduced indigo crystals dissolved in water added at trace.

For this experiment, I boiled 1/8 cup of water in the microwave, then added 1/8 tsp. of pre-reduced indigo crystals and stirred to dissolve. This method still puts off an odor, by the way! This time I made a batch of soap with 16 oz. of oils and poured off 1/2 cup of soap to add 1/4 tsp. of white kaolin clay dispersed in water for some drop swirls (just to add a design element). I took photos of the remaining soap batter after adding increments of 2.5 ml of the indigo solution:

The soap wasn’t poured off after each addition, I simply took a photo each time I mixed in more of the solution.

Once I had 10 ml of indigo solution added, I was happy with the color and poured the soap into the mold, adding the white drop swirls. Instead of putting the soap in the oven, I put it on a heating pad and covered it with towels. This produced a partial gel phase, and you can see the difference in color between the soap that didn’t gel and the soap that did:

No gel on the left, gel on the right

Isn’t it the most beautiful Tiffany blue? I just love how it turned out! I also observed that there is some shadowing around the white drop swirls – possibly due to the migration of the water that dispersed the clay or indigo, I’m not sure which. The other observation is the white outline around the outside of this soap, similar to the outline around the soap made with the crystals in the lye solution. Now I’m starting to think it’s because both of these soaps were made in a mold lined with silicone instead of freezer paper.

I thought I was finished now, but after seeing the results of Experiment #4, I knew I had to try one more batch using the indigo powder from Bramble Berry in the lye solution to see if I could get a nice blue color.

Experiment #5: Testing indigo powder from Bramble Berry in the lye solution.

Instead of adding the powder straight into the hot lye solution, I heated up the distilled water and mixed the powder into the hot water first. I had to cool it down in a cold water bath in my sink before adding the lye. It took an extra step to cool the water down twice, but the powder seemed to incorporate better this way. As soon as the lye was mixed in, the indigo turned a bit green, but you can see that after pouring the solution into the oils, there wasn’t as much residue left:

Lye solution is a dark olive green

Again, this batch size was 16 oz. of oils and I wanted to try one more thing to boost the blue color – layering more colorant into a portion of the soap by adding an oil infusion. I poured off 1 cup of soap and added an oil infusion of 1/2 tsp of indigo mixed with some avocado oil. Here you can see the difference in the color of the raw soap batter:

Oil infused batter is much darker!

And the final soap:

Beautiful gray-green from the lye solution infusion, and dark gray-navy from the added oil infusion.

I can see how layering different amounts of oil infusion on top of a soap that is already colored with indigo in the lye solution could produce some beautiful designs!

In case you are wondering if that dark soap will bleed:

Just noticeable amount of color bleed

Here’s one final comparison photo of the soaps made with 1/2 tsp of powder or crystals in the lye solution of a soap batch size with 16 ounces of oils:

This shows not only the difference in the intensity, but also the shades of greenish-blue to true dark navy.

This has been quite learning experience! I’ve discovered that not all indigo colorants are the same, and that you can achieve different colors and shades using different methods of incorporating the indigo into the soap. I have much more confidence in my ability to color soap naturally with indigo, and I hope you will too!

Secret Feather Swirl soap by Amy Warden