I’m a big fan of soap pigments. They tend to colour my soap very evenly and are easy to use. They are definitely a lot less messy than lakes and micas, and also a little goes a long way. I would strongly suggest to invest in a trio of soap pigments, if you are into cold process soap making!
I use soap pigments from Pure Nature, which are available for $12 per 10 g. They are a bit more expensive than the lakes and micas, but are a lot more economical and will last you for a long time. They stock the basic three colours: yellow, red and blue, which can be easily mixed to create more colours, such as green and blue.
Soap pigments are water-soluble and very easy to work with. The pigments are mixed with water before use, and then added to the soap at trace. If you pre-mix them, you can store them in the fridge for a week. I use these little mini-bottles from Systema for my prepared colours.
I use these bottles in my workshops, and it’s basically add and mix until you get the colour you desire.
The recommended usage rate for these pigments is 0.02%, which is really a very tiny amount. But I found that you can easily double the usage rate to 0.04% without any trouble – meaning no staining and no coloured foam. To calculate the usage rate into workable amounts, I added 2 mini-scoops (0.15CC each) to 3 teaspoons of water, which gives me exactly 0.02% (MATHS: 0.3 ml / 15 ml = 0.02). Add 1 teaspoon of the solution to 500g soap for a 0.02% usage rate, and 2 teaspoons of the solution to 500g soap for a 0.04% usage rate. Is your head spinning yet? In easy terms, mix one small 0.15CC scoop of pigment with 1 teaspoon of water to colour 500 g of soap.
Or do what I do: add 6-8 scoops (0.15CC) to one of the Systema bottles above (or another 30 ml bottle) and fill it water. Then mix and match at trace until you get the colour you desire.
As mentioned earlier, the pigments can be easily mixed to create more colours. For a green, mix one part blue with one part yellow. Add more yellow for a more yellowish grassy green, or more blue for a teal colour. One part red and one part yellow will make orange.
Purples and lavender are a bit more difficult to get right. Purples tend to be more toward the red end of the colour spectrum, so mixing 1/2 red and 1/2 blue usually doesn’t work. With the pigments, I found the ratio 2/3 red to 1/3 blue worked well for me. If you wanted a more reddish purple, you could even increase to 3/4 red to 1/4 blue and increase the usage rate to 0.04%.
Adding titanium dioxide will whiten your soap to make your colour appear more true, as you can see in the picture below. To get the shade of lavender, I added 1/2 teaspoon of titanium dioxide to 500 g of soap.