Learn how to make alkanet root soap, a natural purple soap that can be a lovely lavender to deep purple. Alkanet root is a plant-based ingredient that you can add directly to soap recipes or infuse into a carrier oil. This recipe follows the latter method and is scented with essential oil, and decorated with organic rose petals.
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Although there are soap additives that you can use to make purple soap, many of them are not natural. That’s why alkanet root is such a fantastic purple soap colorant. You still get a vivid lavender to purple color while also sticking with natural plant-based ingredients. Making alkanet root soap isn’t difficult either and is a fascinating process. After many years of making it, I still enjoy watching ruby red infused oil transform into grey to blue soap batter and ultimately purple soap bars. I’ll share how to make it further on along with information on what alkanet is and how much to use in soap.
In this soap recipe, you’ll first extract alkanet root into liquid oil. You’ll then combine it with other ingredients, including gorgeously scented essential oil and dried rose petals, to create handmade soap. This is an olive oil-based soap but also includes coconut oil and castor oil to help create beautiful bubbles. The beeswax helps to harden the bars, and the shea butter makes the soap gentle and conditioning. If you’re new to soap-making, I encourage you to read through my free soap-making for beginners series below.
Natural Soap Making for Beginners
Soapmaking is a fun and creative hobby and here are the basics for understanding more about ingredients, equipment, safety, and how to make soap:
- Natural Soap Ingredients
- Soap Making Equipment & Safety
- Easy Soap Recipes
- Step-by-Step Cold Process Soap Making
Alkanet Root Soap is Naturally Purple
As a natural soap maker, I use essential oils and natural colors in my handmade soap. That includes alkanet root, which arrives from the soap ingredients supplier shredded and dried. Alkanet is a wild plant that grows in Mediterranean climates and produces rich, purple roots. When dried out and then either powdered or shredded, these roots will tint handmade soap from pale lavender to a dark royal purple. That’s because the roots contain a compound called alkannin that is appears red in acidic to neutral pHs, purple in pH 8-9, and blue in highly alkaline environments.
Though you can add ground alkanet directly into your soap, I prefer to infuse a light-colored carrier oil with the roots. Alkanet root is oil-soluble and will readily release ruby-red color in oil. You can used shredded roots to infuse oil or alkanet root powder. It does take time to cold-infuse alkanet root so I can see the alure of using the powder directly in a soap recipe. However, even finely ground, alkanet root can leave speckles and a gritty texture in soap that I’m not a fan of. If you did want to use it, you can use between 1-3 tsp per pound of soapmaking oils (PPO).
Alkanet is a Mediterranean Plant
Some people in Britain are familiar with green alkanet Pentaglottis sempervirens, and it’s the bane of many a gardener. It too is a dye plant but is not the same as the plant we’re going to use. Dyers alkanet Alkanna tinctoria is a low-growing shrubby plant native to the Mediterranean and parts of the Balkans. It has a natural fat-soluble component called alkannin that you can use to naturally color soap purple. Needless to say, it’s non-toxic and skin safe but won’t dye your skin or bathroom.
Though difficult to grow in cool, damp, climates, or in acid soil, you can get a hold of Alkanna tinctoria seeds from a couple of online seed sellers. It’s a rare plant and very picky about where it grows so if you don’t live in a Mediterranean climate it will be very difficult to grow. Alkanet is a perennial plant and if you propagate it successfully, it grows well in alkaline/chalk soils and in climates that are warm and dry.
One thing that you should know is that there is a lot of low-quality alkanet on the market. Sometimes ratanjot Onosma echioides is marketed as dyers alkanet and even looks like it! Unfortunately, it does not have the deep color that you’ll come to expect from alkanna tinctoria. It’s happened to me before and the first indication that I’d been sent ratanjot is that the infused oil didn’t turn ruby red. It was more of a brownish color and the soap it created was a pale pinkish-beige. Not what I wanted at all! The only way to avoid this issue is to only order alkanet root from reputable sellers who specialize in soap making ingredients. In the UK, I always buy my alkanet root from the Soap Kitchen.
Natural Purple Soap Recipe with Alkanet Root
- Stainless steel pan for melting the solid oils
- A large bowl for measuring the liquid oils into
The Soap Making Process
- When I make handmade soap I think of the process as four main parts: Lye solution, Solid oils, Liquid oils, and everything that happens at 'Trace'. Trace is when your oils and lye solution emulsifies and kicks off the saponification phase. Instructions for this recipe are below but you'll find even more detailed information in my free 4-part Natural Soap Making for Beginners Series.
Make the alkanet-infused oil
- Combine 4 g ( 2 TBSP / 0.17 oz) of shredded alkanet root with 255g (8.99 oz) olive oil pomace. I don't recommend using extra virgin olive oil for this recipe because the natural color of the oil will affect the end color of the soap. EVOO is much more yellow-green than lighter-colored pomace olive oil.
- There are two ways to go about extracting the natural purple color from the alkanet roots into the oil. The first takes a little longer but is the way I do it. The second uses heat and will do the job quicker if you're pressed for time.
- Method 1: Combine the alkanet and oil in a glass container and set it in a warm place, out of direct sunlight. Leave to infuse for 4-6 weeks giving the bottle a gentle shake every few days.
- Method 2: Combine the alkanet and oil in a closed jar that will fit inside a slow cooker. Place a small kitchen towel at the bottom of the slow cooker and then place your jar inside. Fill the slow cooker with water just short of the level of the oil in the jar and then set the cooker on low with the lid on. Leave for 10-12 hours or overnight.
- The final step for either method: strain the alkanet root from the oil using a fine-mesh strainer, cheesecloth, or clean nylon. Discard the roots and keep the oil for soap making. The alkanet-infused oil has a shelf-life of the best-by date of the olive oil.
Prepare your Soap Making Station
- Put on your gloves and pre-measure the ingredients. The solid oils into a small stainless steel pan, the water into a heat-proof jug, the lye (sodium hydroxide) into another container, and the liquid oils into another jug. Measure the essential oil into a small ramekin/container.
- Set up your station with your equipment close at hand and now put on your safety goggles.
Make the Lye Solution
- Work in an area with good ventilation when mixing the lye and water together. Pour the lye into the water and then mix with a stainless steel spoon until the lye crystals are fully dissolved. There will be steam and heat in this step so be cautious. Don't breathe in the steam and ensure the lye solution doesn't get on your skin. If it does, rinse it with water thoroughly.
- Set the lye solution aside to cool — I like to set the jug in a basin (or sink) shallowly filled with cold water to speed up the process. Take its temperature with a digital thermometer. You're aiming for it to get down to around 120°F (49°C). It will be much hotter than that initially but keep coming back to stir and take its temperature.
- When the lye solution hits 130°F (54°C), you can stir in the optional sodium lactate. This natural ingredient will help your soap to harden quicker. If you have powdered sodium lactate, use half the amount and make sure to stir it in very well. Keep cooling the lye solution, while also continuing to the next step.
Melt the Solid Oils
- Place the pan of solid oils on the hob and turn it on to the lowest heat setting. It will melt quicker than you expect, so stay with the pan, moving the oil around in the pan to help speed up melting. When there are a few small pieces of solid oil still floating, take the pan off the heat and set it on a potholder. They'll melt with the residual heat and a few stirs of your spoon/spatula.
Add the liquid oils
- Pour the liquid oils into the pan of melted oils. Use your spatula to get every last drop and stir well.
- Take the temperature of the mixed oils. You're aiming for around the same temperature as the lye solution*, but they can be within about ten degrees of one another.
Bringing the Ingredients to 'Trace'
- When the temperatures are right, pour the lye-solution through the sieve and into the pan of oils. All in one go, no need to dawdle. Next, insert your immersion blender's head into the pan at an angle. This allows the air in the head to escape and minimizes air bubbles getting into your soap.
- Stir the contents of the pan gently, using the stick blender as a spoon. Then bring it into the center of the pan and while it's at a standstill, pulse for a couple of seconds. Then gently stir. Repeat this pulse then stir process again and again until the soap thickens up to a light to medium trace. This means that it will be the thickness of warm custard or pudding.
- Don't be alarmed at the color of your soap right now — it will likely be grey or a greeny-blue-grey. This is completely normal and the color will change to purple over time.
- The soap will keep thickening up at this point so work quickly. Pour the essential oil into the soap and stir it together thoroughly. Then pour it into the silicone loaf mold. It should only fill the mold partially. Settle the soap so that it has a flat top. You do this by gently tapping the mold on the counter.
- Next, turn your oven on to the lowest heat setting. This is to create a warm environment to help the soap to gel and the purple color intensify.
- The final touch is laying your dried rose petals on top, though this step is optional. When sprinkling the petals on, make sure to think about how you want to cut the loaf up into bars. When this is finished, place the soap into the oven and make sure to turn the oven off.
Cutting and Curing
- Leave the soap in its mold for 48 hours. After this point, the soap will be the consistency of cheddar and will have almost fully completed saponification.
- Take it out of the mold with gloved hands and, in the case of a loaf, cut it into bars of the size you wish. A ruler helps here if you want bars all of the same size. Also, you may wish to cut your bars from the bottom of the loaf towards the top. This avoids drag marks from the rose petals being pulled by the knife through your block of soap.
- Next, find someplace in the house that's safe from animals and kids and that is airy and out of direct sunlight. Lay a piece of baking paper down and space your bars of soap out over it. You should leave your soap there for four to six weeks to allow excess water to evaporate out of your soap and for them to fully harden. This is called curing soap. When fully cured, you can begin using the soap and gifting it to others.
- Be aware that the color of your soap may look different from the point you cut it, to the point that it's ready to use. The purple color will continue to change over the curing time and the insides of your bars will eventually match the color of the outsides.
- Once made and cured, your soap can 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. Cold-process soap should be stored in the open during that time, as the natural glycerin in the bars can draw moisture to them if you put them in a sealed container.
Learn How to Naturally Color Soap
Alkanet root soap isn’t the only natural purple soap you can make. You can also use gromwell root, Brazillian purple clay, and a few other ingredients. Here’s more inspiration on making beautiful handmade soap in a range of natural colors:
- How to Naturally Color Soap With Clay (Earthy Soap Colorants)
- Charts of Natural Soap Colorants Listed by Color
- Simple Olive Oil Soap Recipe
- Pumpkin Spice Soap Recipe (naturally yellow)