How to Make Natural Purple Soap with Alkanet Root
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.
This page may contain affiliate links. As an Amazon Associate I earn from qualifying purchases.
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
Equipment
- Stainless steel pan for melting the solid oils
- A large bowl for measuring the liquid oils into
Ingredients
For the alkanet-infused oil
Lye solution
- 47 g Sodium hydroxide 1.66 oz
- 85 g Distilled water 3 oz
- 1/2 tsp Sodium lactate (optional) liquid sodium lactate
Solid oils
- 88 g Coconut oil (refined) 3.1 oz
- 11 g Shea butter 0.39 oz
- 7 g Beeswax 0.25 oz
Liquid oils
- 227 g Olive pomace oil 8 oz – infused with alkanet root
- 18 g Castor oil 0.63 oz
Add after Trace
- 1.5 tsp Rose Geranium essential oil 7 g
- dried Rose Petals to decorate
Instructions
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.
After Trace
- 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.
Notes
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)
Hello, love your recipes. I Made an alkanet powder infusion with olive oil (1:10). One tablespoon was equivalent of 6-7 grams. Do I need to replace just a part of the olive oil? Or can I use 255 gr of my infusion for this recipe?
Kind Regards
Katja
Hi Katja, the recipe calls for 227 g of alkanet-infused olive oil. However, when you make the infused oil, the alkanet pieces will absorb oil that you won’t be able to get back out. That’s why there’s a larger amount of olive oil in the infusion step — so that when you strain it, you will get enough olive oil (227 g) for the recipe.
Using the Alkanet root powder mixed into the Pomace olive oil was a great idea. I carefully place the Alkanet powder into an empty, clean tea bag, and placed it in the oil to to seep. The container that I used was a sterilized mason jar (and stored in a cool dark cupboard) for about 2 weeks before straining the mixture. The rich shade of deep red oil changed into a gorgeous green-blue color once my oils were mixed with the lye. I used frozen goats milk with my lye in my recipe, and I can not wait to see the outcome in 4-6 weeks. Thank you for the idea and recipe.
I infused 1tsp of alkanet root powder with my melting hard oils, strained and got a beautiful red burgundy… but then when I mixed the lye with the oils it turned into a blue/green! Will this change over time? I can’t possibly see how this could turn to purple… I was trying to make a lavender soap
It’s completely normal, so don’t worry. You’ll be amazed to see your soap turn purple over time :)
Hi,
I love all your recipes, most of them turned out great.
I still didn’t manage to obtain a purple one and I was thinking to try this one out but I would like to leave out the beeswax or replace that with something vegan?
Is there any alternative?
Thank you x
Hi Monica, you can use alkanet root for almost any soap recipe including this one that’s both eco-friendly and vegan. Make the recipe as usual, but replace ordinary olive oil for alkanet-infused olive oil :)
Hi Tanya,
I was actually asking if I can replace bees wax with soy wax for example or just leave it out. Would this affect the colour of my soap?
Hi Monica, unfortunately, from-scratch soap recipes cannot be altered like that. Change one ingredient and the entire recipe would need to be recalculated, and the lye amount adjusted. That’s because each individual oil, wax, and fat needs a specific amount of lye to transform it into soap. For more info, please read this piece on changing and customizing a soap recipe.
Hi,
Could Coconut Oil be used to infuse the Alkanet Root instead of the Olive Oil.
Thanks
Joy
Only if the coconut is kept melted (warm), but you could do that in a crockpot. Infusing it in a liquid carrier oil, like olive oil, is easier and doesn’t use electricity.
Hi,
Mine had a great color after pouring, but the next day, one of the molds turned brown and the other not…
Tanya, what do you mean “oil wasn’t infused for long enough” how long its supposed to be infused?
Thanks
Ariela
Hi Ariela, I’m not sure what’s going on with your molds. Are you using metal molds? Infusing oils — alkanet needs a good two weeks to infuse at the bare minimum. I often will leave my oils to sit with alkanet for two months beforehand. If you don’t get good color even after that time, it’s possible that the quality of the alkanet is poor.
Hi Tanya,
this is one of many recipes I have tried from your website – I really like it. In previous comments it says, that the grey colour will change over time to purple. My soap is 48 hours old now, and is still grey. Can you please specify the time till it turns purple? How long does it take? I am getting a bit worried, it is not a “nice grey”…
Thanks a lot, Jarka
Hi Jarka. If there’s not even a hint of purple now, it’s unlikely to come through. There are three things that could have gone wrong, 1. The alkanet you used was poor quality, and unfortunately, a lot of what’s sold can be. I recently had a bad batch of it sent to me from my regular supplier so it does happen. How do you know? The infused liquid oil won’t be red in colour but more of an orangey-brown. 2. You used extra virgin olive oil. The natural green colour of the oil competes with the purple of the alkanet, resulting in a murky colour. Try again using pomace olive oil or light coloured olive oil. 3. The oil wasn’t infused for long enough.
What proportion of infused oil do you use for the colour in the picture? The instructions aren’t clear, leading to believe all the olive oil is infused, but then a picture caption says to use all infused for a more vibrant colour!
All the olive oil should be infused with alkanet for this recipe.
Hi Tanya, thank you so much for your great recipes.
I wonder if you can help me, I’ve made this soap with alkenet infused in the olive oil. Everything seemed ok then while curing on my rack it seems to have developed whitish spots all different sizes about the size of an end of a pencil and smaller.
Do you know what it could be?
I would post a pic but can’t work out how to do it.
Thank you x?
There are two things that I suspect it might be. First you need to make sure that they’re not chunks of undissolved lye. Have you tried the zap test with them yet? Also dig a few pieces out and put them on a paper towel. Wet them and see what happens. If the paper towel turns brown then they’re lye. In that case you can grate the soap up and rebatch it in a crockpot.
It could also be that they’re stearic spots. This is a natural component of many oils and if you mix your soap at too low a temperature they can form.
Lastly — did you use a fragrance oil (opposed to an essential oil)? Some can cause what is called ‘Ricing’ which are white spots of all different sizes which sounds to me like what you have. Did your soap look like cream of wheat or porridge when you were bringing it to Trace? If it is ricing, it’s caused by components in the FO bonding to some of the harder components in your recipe. Perhaps tiny pieces of alkanet that weren’t strained out. Ricing is more of a cosmetic issue and the soap can still be used. You might want to consider rebatching it if you don’t like the look though.
Thanks for your reply Tanya,
I’ve done zap and paper towel test and both were ok…. I also used essential oil, once with geranium essential oil and other with lavender essential oil.
The only time its happened is when I used the alkanet infused oil, which Is twice now, I wonder if that has something to do with it ?
Your Lemongrass soap and goats milk soap came our great. Thank you ?
P.s what is the best way to rebates soap
Alkanet on its own doesn’t leave spots — I suspect that they’re stearic spots as described before. There’s a lot more information online if you wanted to reasearch it.
There’s general instructions on how to rebatch soap in point 2 of this piece: https://lovelygreens.com/5-ways-to-make-handmade-soap/
Could it be that she soaped at a too low a temperature and the beeswax started to solidify? I’ve had this happen to me with my beeswax soap and it requires a warmer soaping temperature than regular cold process soap.
Sorry for replying so late, this is just in case it helps someone else. These spots can also very well be bubbles, tiny bubbles that get trapped in the batter and show later as white spots upon cutting. Try getting a needle and poke one to see if there’s a tiny hole there, or look very closely with a magnifying glass.
To prevent this from happening, pour your clear lye solution down the shaft of the blender, burp the blender before turning it on and just beware of anything that might introduce air in the batter.
I made a very similar recipe and my dried rose petals ending up turning brown and now the soap looks so ugly. My go to recipe is 80% olive oil, 10% palm oil and 10% coconut oil. I used rose geranium EO. What did you think caused the discoloration?
I suspect that it’s heat. I’d suggest not placing the towel over your batch if you’re making more than the amounts listed in this recipe. If you double/triple the batch there will be more heat in the loaf. That means more heat when you insulate it. It’s great for getting that rich purple colour in the soap but does cause the petals to brown.
If you are using alkanet root “powder”, how much would you put in the oil instead of the dried matter??
The same amount in grams
Thank you so much for sharing your knowledge! What if you are using alkanet root powder. What is a good ration for this lovely purple?
I don’t use Alkanet root powder directly in soap since the texture can be a little scratchy. If you’re looking for an exfoliating soap then go for it and experiment — otherwise I’d recommend you stick with infusing the oils. You can use both the whole roots or the powder to infuse your oil.
Thank you for responding and thank you for all your input and teaching. It really helps me as a new soaper all the way from Texas.
My pleasure!
Hi Tanya, I love your website and all the great Info. We made our first soap this great soap with alkanet yesterday, it smells great, looks bit different in color, more like grey-blue. We have the only problem to cut it, used the extra virgin oil olive and coconut and in milk box. It is tricky to cut it in actual size we like to have, what could be the issue? as I really like to try also others, I would be glad if you could give me a hint. we use castor oil which smell quite unplesent in background do you have some suggestion for it or to switching it with other oil? thanks a lot
Monika
Hi Monika! The blue-grey is normal at first and will change to purple over time. As for cutting it, did you change the recipe at all? With soap recipes you cannot deviate from the exact ingredients. In any case, the recipe is sticky in its first couple of weeks if you didn’t use the optional sodium lactate. Just wait that amount of time before cutting it up. Lastly, Castor oil should not smell unpleasant — could it be that you used old oil and that it’s gone rancid?
thanks a lot, looks like the alkanet was poor quality, because it really was more of an orange-brown…neverthelss, thank for beautiful recipes and detailed instructions
It happens, unfortunately. If you purchased your alkanet from a beauty supplier, consider getting in touch and asking for a refund.