A month before you make this calendula soap recipe, start infusing the olive oil with dried calendula flowers. Make sure that the petals are orange, not yellow. For this recipe, I used 25 g dried flowers to 500 g olive oil. You can eyeball it though if you wish as described further above.
Mix the calendula and oil together in a sealed jar and leave them to steep in a dark but warm place for a month. Give the jar a shake every now and again.
After a month, strain the flowers from the oil and discard (compost). You will have enough orange-tinted calendula oil to use for two batches of this soap recipe. Or you can use whatever you have left to make this salve.
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.
Set out your mold and ensure you have everything you need laid out. Being organized at this stage will help you to successfully make soap!
Make the calendula soap
The first step is to 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 lye-water and the oils. You should aim to cool them both to be 100°F / 38°C, or just below.
Pour the lye solution into the pan of oils. I recommend pouring the liquid through a sieve to catch any potential undissolved lye. The soap mix will still look somewhat transparent until you begin mixing it.
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 and look of it will be like thin custard.
Stir in the essential oil, if you're using it. Mix thoroughly, but quickly. Essential oil adds scent to your soap but it's an optional ingredient and you can leave it out if you'd like unscented bars.
Still working quickly, pour the soap into the mold(s). Give it a tap to settle it. If you wish, you can sprinkle dried calendula flower petals on top. If you live in a humid climate, don't do this, since any kind of botanicals in/on your soap can mold.
Take steps to ensure that the soap gels. This is a process where the soap heats up and the color deepens and is important if you want bright colors. There are a couple of ways to do this but the best I've found is to place the mold in an oven that has been preheated to about 100°C (212°F). Turn the oven off and close the door. Leave the soap inside for at least 12 hours, or overnight.
The next day, take the soap out of the oven and set it someplace to rest for another day.
Once 48 hours have passed, you can take the soap out of the mold and cut it into bars using a soap cutter or kitchen knife. If you've opted to decorate the top with flower petals, cut the loaf from the bottom, to avoid dragging the petals through the soap with your knife.
You can get five or six decent-sized bars of soap from this batch if you use the square mold that I have. In the six-cavity molds, you'll get six perfect bars, but it can be more challenging to gel the soap.
Cure it 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.
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.