An easy indigo soap recipe for creating natural blue soap with blue indigo pigment. Also, tips on making soap with indigo-infused oil. Indigo is an excellent natural soap colorant for blues that ranges from pale blue to deep denim. Includes an introduction to the differences between blue and green indigo powder in soapmaking.
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Naturally coloring handmade soap is like layering magic over magic. The soapmaking process in itself is pretty amazing, but using leaves, roots, flowers, and clay to tint soap stunning hues is a whole other ball game. I share plenty of natural soap coloring ideas here on Lovely Greens, but one that I’m really excited about is this indigo soap recipe. Recipe isn’t quite the word for it, though, since it’s really two methods that you can use to create naturally blue soap. Methods that you could use for almost any natural soap recipe. I also introduce a third way to create a unique blue shade by using two different types of indigo.
The instructions below are for cold-process soap recipes. You could use any light-colored soap recipe of your choice, but avoid using those high in golden or dark-colored oils. The color of those ingredients may tint your soap greenish. Also, have care that you use true plant-based indigo to naturally color soap. Synthetic indigo is much more common but is not safe to use in soap or personal care products.
Natural Blue Soap Recipe
I first introduced you to making a natural blue soap in my woad soap recipe. Though the soap woad creates is a lovely natural denim color, you need a lot more powder, and the final color is less vibrant than if you used indigo. Woad soap has a softer hue that I love, and that definitely has its place. This indigo soap recipe will give you much deeper shades, including a rich denim blue and a baby blue.
Used both on the skin and in dyeing fibers, woad (Isatis tinctoria) and indigo (various species, including Indigofera tinctoria) are safe dye plants with a long history of use. Both are rich in compounds that are indigo precursors and how humans learned to extract it from leaves boggles my mind. That’s because extracting it from green leaves yourself can be a lengthy process. I found that out myself this year when I grew Japanese indigo Persicaria tinctoria. Indigo pigment extraction is a beautiful and fascinating art, but if you don’t have the time, you can purchase ready-to-use powder. Blue indigo pigment is ideal for dyeing cloth, using in artwork, and naturally coloring soap.
For natural blue soap, I’ve begun with indigo powder purchased from a natural textile dyer. A tiny amount of this deep blue powder goes a long way, and beware, it can be messy! One of my plastic jugs is still blue from using it. To get the darker blue soap in the photo above, I added indigo during the soapmaking process. To get the lighter blue soap, I first infused the indigo in liquid oil for six weeks.
Indigo is a Natural Dye Plant
There are many species of plant that we commonly call indigo, but the one I’m using in this recipe is Indigofera tinctoria. When working with plants or plant-based materials, it’s important to always identify it by its Latin name rather than a common one. That’s especially true when it comes to using them on or in our bodies.
If you’d like to try growing and using homegrown Indigofera tinctoria, know that its home is in the tropics. That means that you need to have a humid and hot climate or be able to mimic those conditions with a polytunnel or greenhouse. If your climate is more temperate, Japanese indigo might be a better choice for you. It grew perfectly in my polytunnel, though our outdoor temperatures here are never more than about 84F. See photos and Japanese indigo growing tips in my piece on indigo pigment extraction.
Indigo Indigofera tinctoria is a perennial broadleaf evergreen that can grow six feet (2 m) tall in the right place and with the right care. It has beautiful pink flowers, and Teresinha Roberts of Wildcolours recommends harvesting leaves just before they open. She also says that you might not be able to harvest from your plants until they’re at the end of their second year of growth, and at that time, you should only take half or less of the leaves.
How to use Indigo in Soap Recipes
Creating natural blue soap with indigo is relatively easy, and there are a few ways to do it. The easiest way is to mix a small amount of indigo powder into part of your liquid oil in a soap recipe. You can then stir that blue oil in at trace and pour the blue soap batter into the mold. If you ensure that the soap fully gels, then the color will be much more intense.
When I say a small amount, it means less than 1/2 tsp per pound (454g) of your main soapmaking oils, and it’s best to pour the colored oil through a sieve to remove any clumps. Use more than that, and your bars will be very dark blue, but the lather will also be blue and could stain your bathtub or washcloths. Clumps of indigo will freckle your soap and may come off while you wash.
To get an even more intense color, don’t wait to add the indigo at trace. Mix the powder with the sodium hydroxide, then make your lye solution with it as usual. You will notice a pungent scent when you make your lye solution with indigo, but that scent doesn’t last in the bars. Adding indigo to the lye solution seems by far to be the most popular method that soapmakers use. The color is more vivid, but the downside is that all of your soap will be the same deep color. I love simple soap designs, so that’s fine by me, but if you want to add swirls or layers to your batch, you might want the first method.
Making Indigo Soap with Infused Oil
To make pale blue bars of indigo soap, I used a different method. While indigo isn’t particularly water-soluble, it will infuse into liquid carrier oils. All of the pomace olive oil I used to make this batch was infused with indigo and the lovely turquoise color you see in the spoon. To make indigo-infused oil, I combined 1/2 tsp indigo with 17.6 oz / 500g pomace olive oil. Pomace olive oil is important since it’s lighter in color than extra virgin, and so won’t interfere with the final color. I left the glass jar in a dim place and gave it a shake every few days. I did this for a month before using the indigo-infused oil as part of a soap recipe.
To make indigo soap with infused oil, don’t shake the jar of oil on the soapmaking day. Instead, gently pour off the amount of oil you need, leaving the indigo sediment at the bottom of the jar. Make your batch of soap (this is the recipe I used), as usual, replacing the ordinary olive oil in the recipe for the indigo-infused oil. Though you could use just a partial replacement, go for it and replace all of it if you wish. Also, ensure that the soap gels if you want to get the best color.
Another way that soapmakers use indigo is by making an indigo reduction. In a stainless steel pan, add one Tablespoon of indigo powder to half a cup of distilled water. Bring to a boil and reduce by half, or until the liquid has the consistency of ink. Add this reduction by the drop, at trace, until you get the color you want.
Why is my Indigo Powder Green?
Indigo isn’t widely used as a natural soap colorant, but it is used for two other reasons — to dye cloth blue and to dye hair black. You can get a hold of pure indigo in either sector, but you’ll notice that the two look completely different. The indigo purchased for hair dyeing is green and is simply the dried and crushed leaves of the indigo plant. You can use it together with henna to tint hair black, but it will not color your soap blue. Instead, it can tint soap a greenish-tan color that reminds me of dead sea clay powder.
Deep blue indigo powder is what you need to naturally color soap blue. This indigo comes from the same plant as the green indigo but is soaked in water, fermented, and treated with lime to bring out that brilliant blue hue. The outcome of the indigo pigment extraction process is a paste that can be dried and pulsed into powder. Though it is possible to ferment green indigo powder to create blue dye, I’ve not tried it. I do know that the color potential will be far lower than if you use fresh indigo leaves or blue indigo pigment powder, though.
Use both Green and Blue Indigo in Soapmaking
I wasn’t able to find any photos of what green indigo soap looked like, so I tried making it myself. The photo you see above has the result of that test batch at left. To achieve that greenish-gray shade, I mixed 1 tsp of green indigo into part of the olive oil for that 1-lb soap recipe. I added it at trace and oven-processed it to ensure it gelled. It came out of the mold that color and has retained that shade now for well over a month. Not everyone will like the color, but I certainly do! It’s a modern and elegant neutral shade that I think would work well for my neem soap recipe.
It got me thinking, too. What would happen if I mixed the green indigo with the blue? The result is the third soap (from the left) in the photo above. It creates a lovely sage blue that, again, seems very modern and natural. It is an earthier blue compared to the blues achieved with just indigo. For the sage-blue soap below, I made a 1-lb batch of my eco-friendly soap recipe (I used this recipe for all of the indigo soap batches). At trace, I added 1/2 tsp of green indigo and 1/8 tsp blue indigo that I’d mixed into a Tablespoon of the reserved pomace olive oil.
Indigo Soap Recipe
Let’s get to using indigo to make a clean blue shade, though. The recipe below includes instructions on adding indigo pigment powder to the lye solution and creating single-color blue bars. Though some soapmakers have reported the color of their indigo soap fading over time, I’ve not seen this happen. It may have to do with the quality of the indigo or how it was stored.
Naturally Coloring Cold Process Soap
- Himalayan Rhubarb Soap Recipe (Magenta-red)
- Calendula Soap Recipe (Yellow)
- Annatto Seed Soap Recipe (Orange)
- Alkanet Soap Recipe (Purple)
- Watch the Indigo Pigment Extraction video
Indigo Soap Recipe (lye-solution method)
- Stainless steel pan for melting the solid oils
- A large bowl for measuring the liquid oils into
- Prepare your workstation with your tools and equipment. Put on rubber gloves, eye protection, and an apron. Carefully pre-measure the ingredients. The solid oils into the pan, the liquid oils into a jug, the water into another heat-proof jug, and the lye in another container.
- Stir the indigo into the dry lye crystals. Indigo doesn't disperse very well in water and you'll notice that after the next step. Mixing the indigo with the lye at this point will help with clumping though.
- Next, dissolve the lye (Sodium hydroxide) crystals in water. In an airy place, outdoors is best, pour the lye crystals into the water and stir well. There will be a lot of heat and steam so be careful. Try not to breathe it in. Leave outside in a safe place, or in a shallow basin of water to cool.
- Melt the solid oils in a stainless steel pan on very low heat. When melted, remove from the heat and set on a potholder. Pour in the liquid oils. If you have the olive and castor oils in the same container, stir them together first before pouring into the pan. Castor oil is pretty sticky and it's easier to pour when mixed with a lighter oil.
- Measure the temperatures of the indigo lye-water and the oils. You should aim to cool them to about 110-120°F / 43-49°C.
- Add the indigo lye solution to the pan of oils. To avoid creating air bubbles, pour the lye solution against the side of your stick blender or a spatula. This slow and steady pouring method is what soapmakers do to create professional-looking bars with fewer imperfections.
- Dip your immersion blender into the pan and with it turned off, stir the mixture. Next, bring it to the center of the pan, and with both your hands, hold it on the bottom of the pan and blitz it for just a couple of seconds. Turn it off and stir the soap batter, using the blender as a spoon. Repeat until the mixture thickens up to 'Trace'. This is when the batter leaves a distinguishable trail on the surface. The consistency will be like thin custard.
- Working quickly, pour the soap into the mold. Give it a tap to settle it. I'm using the six-cavity silicone mold listed in the equipment list for this recipe. Feel free to use another of your choice though.
- Ensure your soap gels to get a truly vivid blue soap. With smallish silicone cavity molds it's a little trickier to gel soap than in loaf or larger molds. What I do is place the mold on a thick wooden cutting board (it's advisable to protect the wood with a layer of grease-proof paper). Then I put it in the oven at 170°F / 77°C and keep it at that temperature for at least half an hour, if not a full hour. I judge the time by having a peek every now and again and checking to see that the soap batter turns a dark color throughout. After that, I'll turn the oven off and leave the soap inside overnight.
- The next day, take the soap out of the oven and set someplace to rest for another day. Once 48 hours have passed, pop the soap out of the mold.
- Cure the bars for 28 days. Curing means leaving the bars spaced out on a protected surface out of direct sunlight and in an airy place. This allows the extra water content to fully evaporate out. Here are full instructions on how to cure soap.