Use this woad soap recipe to make natural blue soap with specks of darker blue throughout. Part of the naturally coloring handmade soap series.
There’s nothing quite like growing a plant, nurturing it through its life, then finally using it in the kitchen or creative pursuit. A full circle of growing, harvesting, making, and finally using that has as much to do with the plate as with the soap draining dish. As you can guess, my main interest, aside from kitchen gardening, is making natural handmade soap. Blending raw ingredients like oils, dried herbs, and plant-essences to make beautiful bars using deliberate, skin-safe ingredients.
Beautiful is a keyword here. There are soap makers out there who stick with basic soap recipes that are more function than form. Useful laundry soap, soap for washing dishes, simple body soap, and the like. There’s nothing wrong with that at all. For most of my soap, I like to add a little more creativity though, and that involves naturally coloring it.
Naturally coloring soap blue
It’s possible to get a relatively complete range of colors in handmade soap by using plants and clays. That includes spices, seeds, bark, roots, and leaves. You use various techniques to extract or use the color – some easier than others. One easy way is by adding Cambrian blue clay to your soap base. It’s a pretty shade that’s predictable and goes well with herbal essential oils.
Woad Isatis tinctoria, on the other hand, can be a little more involved. The pigment is in the long deep green leaves of the plant but needs extracting before you can use it in soap. I go over how it’s done in another piece. To skip this step, you can purchase woad powder from a reputable source. One such source in the UK is Teresinha Roberts, who grows and processes it herself. Woad for soap making is a deep blue and very fine powder.
Woad, a natural dye plant
When the Romans arrived in Britain in 55BC, they found the residents painted and decorated with woad. Caesar wrote that Britons “dye their bodies with woad, which produces a blue color,” and Pliny recorded that many of the women “stain all the body” blue with woad (an intriguing thought!). Another source, Claudian, a Roman poet, later described Britannia as being decorated with tattoos and dressed in an azure cloak. These are our first known references to woad as a dye plant.
Eventually, woad became commonplace as natural wool and fiber dye across Europe. It was only in the last five hundred years that it was replaced as a dye by indigo. Indigo itself was then replaced in modern times by synthetic blue dyes. Still, woad persists as an artisanal dye with those who work with natural fibers and cloth. More recently, soap makers have experimented with it as well. While it’s difficult to achieve the vivid blues and blue-greens of fiber dyeing, woad will naturally tint soap a pale blue-green, to pale blue, to deep denim. It’s a natural and soft blue in all its hues.
How to naturally color soap with woad
There are three ways to use woad to naturally color soap blue. No matter which method you try, begin with a soap recipe that doesn’t include a lot of yellow or golden oils. The reason being is golden oils naturally create cream to pale yellow colored bars. This warm color will interact with woad, giving you green bars in the end — it’s like mixing blue paint with yellow. So avoid extra virgin olive oil and other dark oils and butters and use recipes that include coconut oil, shea butter, and light-colored liquid oils such as olive oil pomace.
You can introduce woad to the mix by adding the powder directly to the lye-solution, infusing the liquid oils with it, or adding the powder directly to the soap batter. You can get a much darker color if you add the powder to the lye-solution and the warm liquid helps the color to become a kind of blue tea. That can help more of the color to be expressed in the final soap.
Woad Soap Recipe
- Stainless steel pan for melting the solid oils
- A large bowl for measuring the liquid oils into
- 64 g Sodium hydroxide 2.26 oz
- 120 g Distilled water 4.23 oz
- 4 g Woad 1 tsp
- Soap making is fun and creative but it's also chemistry. Make sure your workspace is set up with your pre-measured ingredients and that you're wearing appropriate clothing, footwear, and safety gear. Always wear goggles and rubber gloves when handling lye or the soap batter.
- Dissolve the lye (Sodium hydroxide) crystals in the water. In an airy place pour the lye crystals into the water and stir well. I prefer doing this step outdoors when possible because of the steam that will come off it initially. It's not pleasant if you accidentally breathe it in so avoid this by holding the jug well away from you.
- When fully mixed, add the woad powder to the lye solution and stir well. Leave the lye-solution to cool in a safe place. I usually set the jug in cool water that I've run in the sink. Ensure that children and animals cannot get into it and be careful around it yourself. Never handle it without your gloves and goggles one.
- 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 and stir.
- Measure the temperatures of the lye-water and the oils. You should aim to cool them both to be about 100°F / 38°C. You don't need to be on the dot but aim to have them at that temperature or slightly cooler. The oils and the lye solution should be within ten degrees of one of another.
- While you're balancing the temperatures of the oil and lye solution, pre-heat the oven to 100°F / 38°C. I find that if I put it on at the lowest setting, this takes only a minute or two. Turn the oven off after and keep the door closed.
- When your ingredients are the right temperature, put your gloves and goggles back on if you've taken them off. Pour the lye solution into the pan of oils.
- 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, press it to the bottom of the pan and blitz it for just a couple 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 distinguishable trails on the surface. The consistency will be like thin custard at first but it will thicken quickly so make sure to work quickly after this point.
- Next, add the essential oil and gently stir it in. It's for fragrance and completely optional. You could use other scents as well but make sure to follow the rules outlined in this piece.
- Lay your soap mold(s) out on a baking tray lined with baking paper. Next, pour the soap into the molds. Give them a tap or jiggle to settle the surface. Pop the molds with the tray in the oven and leave them there for a full day. Don't be tempted to open the oven during that time since heat will be lost. That initial warmth that gradually fades away is important to achieve a deep color.
- The next day, pop your bars from the mold(s), cut them into bars if required, and cure them for four weeks. 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. It also allows the bars to harden up.
- Once made, your soap will have a shelf-life of up to two years. Check the oil bottles that you're using though -- the closest best-by date is the best-by date of your soap.