When it comes to making soaps, you have a lot of colouring options available to you. Out of these, there are four that are the most common: ultramarines, iron oxides, micas, and fluorescent pigments. Here is a brief overview of these different types of colourants and when to use each one.
Iron Oxides and Ultramarines
Iron oxides and ultramarines are pigments that are processed in labs. While they were originally mined, today they are processed in labs in order to ensure purity. In the case of iron oxides, these pigments must be made in a lab because raw iron oxides are often stuck with toxic metals, such as arsenic, lead, mercury, antimony, and selenium. Processing them in a lab ensures that toxic metals are only present in low concentrations that are considered to be safe.
The good thing about using these pigments in soap is that they are mostly stable, meaning that they will not change colour in cold process or melt and pour soap. They are also available at a cost-effective price so that you can obtain the colours that you need to prepare a large batch of soap at a reasonable price.
However, one drawback of using ultramarines or iron oxides as pigments is that you need to take extra care to avoid clumping. Using a hand mixer to pre-mix your pigments in some deodorised fixed oil before you add them to your soap should help to remove any clumps. Then they can be added to cold process soap. For melt and pour soap, the pigment should first ideally be mixed thoroughly with glycerine to get rid of speckling and can then simply be added to the soap.
Fluorescent Pigments
Fluorescent pigments are very bright and give your application an extra wow factor. They are excellent for use in making soap because they provide uniform colouring that remains consistent from batch to batch.
Although, fluorescent pigments also tend to clump, the clumps can be easily removed with pre-mixing. Use them by themselves or to brighten the tone of other colours. However, take care when using fluorescent pigments as there may be violent or incandescent reaction of the product with metals, such as aluminium, magnesium, potassium, zinc, lithium, sodium etc, at high temperatures.
Micas
Mica is a naturally occurring product that can be mined. It is then coated with pigments to achieve the desired colour. Mica is commonly found in makeup, including lipstick, blush, and eye shadow. The best part about using micas is that they don't clump at all.
However, the combination of micas with other colorants means that they may or may not be stable in certain soaps and will require testing. Generally, they work best in clear melt and pour soaps. This allows the shimmer to attract the light that it needs to reflect and refract.
Always take care when handling pigments and avoid spills whenever possible. Powders can create dust and settle on surfaces where moisture in the air cause them to bleed their colour into the surface, creating damage that is difficult to clean. Additionally, you should always wear a face mask when handling pigments, as well as, disposable gloves.