Cold-process soap recipe using woad powder to naturally color the soap blue. Measurements are in weight and a single batch makes five to six bars. Technical information: 1lb / 454g batch -- 5% superfat -- ~34.5% lye solution
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.