Synthetic dyes for soap: mica, oxides and pigments

TL;DR: Synthetic colorants (mica, oxides, pigments) are the most reliable choice for consistent, richly colored soaps. They do not fade and do not oxidize during aging. Three main groups: mica (metallic effects), oxides (stable base colours), synthetic pigments (variant but with risks). Always test with soap safe test before using in a full batch.

Synthetic dyes are the most reliable way to achieve a consistent, richly colored soap collection. Unlike natural alternatives, they don't fade, oxidize or undergo alkaline degradation - the color you see in your finished soap in a year is the same as the first week.

But not every synthetic dye is suitable for the alkaline environment of CP soap. Choosing the wrong pigment can cause color bleeding, fading or unexpected discoloration. This page takes you through the three main groups and shows you how to work with each.

Three groups of synthetic dyes

What is mica and what dyes it?

Mica is a naturally occurring mineral silicate - mica - crushed into a very fine powder. Natural mica is white or translucent. Commercially sold cosmetic grade mica is coated with metal oxides (titanium dioxide, iron oxides) or synthetic fluorescent paints - this gives the mica its colour effect and metallic sheen.

Features:

• Fine texture, smooth spread
• Metallic or pearlescent appearance
• Colour range: hundreds of shades from white to gold, bronze, electric blue, purple to black
• In soap: loses metallic shine and becomes duller (surface alkalisation)

Stability in CP soap: Depends on the composition. Pure mineral micas (iron oxide + mica) are stable. Micas with fluorescent colors (neon, ultraviolet) may change to a different color or fade in alkaline environments.

Dosage: 1 teaspoon (approximately 3-4 g) per 500 g of oils. For a metallic effect on the surface, less is enough, for a rich cross-section color use 2 tsp.

What are metal oxides and why are they the most stable?

Oxides are inorganic pigments - the most stable dyes for CP soap. Originally extracted from mineral deposits, they are now synthetically produced for cosmetic use (purer composition without natural impurities).

Basic types:

Iron oxides:

• Red iron oxide (CI 77491): terracotta to reddish brown
• Yellow iron oxide (CI 77492): deep yellow to ochre
• Black iron oxide (CI 77499): grey to black
• Combine the three to achieve the full spectrum of brown, beige and leather

Ultramarine (ultramarine):

• Blue ultramarine (CI 77007): deep blue
• Purple ultramarine: purple
• Pink ultramarine: soft warm pink
• Originally mined from lapis lazuli, now synthetic
• Caution: ultramarine reacts with acids - in a very acidic environment or when added to a leaching solution it decomposes and may disappear

Chromium oxide green (CI 77288): Stable dark green, slightly earthy tone.

Chromium hydroxide green (CI 77289): Richer green, less earthy.

Oxide dosage: 0.5-1 teaspoon per 500 g of oils. Oxides are intense - small amounts dye strongly. Start with 0.5 tsp and adjust.

Which synthetic pigments are suitable and which are not?

This category includes a broad group of organic synthetic dyes:

Chromium-based lakes and synthetic pigments: Stable in soap, approved for cosmetic use according to EU regulation.

FD&C a D&C barviva: Barviva původně schválená pro potravinářství (FD&C) nebo pouze pro kosmetiku a léky (D&C). Většina z nich NOT suitable for CP soap - are hydrophilic and fade or morph to unexpected colours in alkaline environments.

Exception: Některé D&C lakes (pigmentové soli) jsou stabilnější než jejich mateřská barviva — ale vždy ověřte u dodavatele testování v alkalickém prostředí.

How to test the suitability of the dye?

What is a soap safe test and how is it done?

Before using a new dye in a whole batch, test it:

Testing procedure:

1. Prepare a small test cupcake soap (100 g oils, 1 tsp dye).
2. After curing and 48 hours, check the colour - does it match expectations?
3. After 4 weeks of maturing, check again - has the colour changed? Is the pigment bleeding?
4. Try wiping the surface with a damp white towel - does it stain?

Bleeding of colors (bleeding): Some micas and pigments migrate to adjacent colour layers. Bleed-prone dyes are not suitable for multi-colour design - they can only be used in single-colour soaps or as surface sprinkles (where bleeding is not an issue).

Bleeding test:

Make a two-color test soap - test dye next to white soap (titanium dioxide). After 4 weeks, cut and check the color interface.

EU regulation of cosmetic colours

What do I have to follow if I want to sell soap with dyes?

Strict conditions apply to the sale of soap as a cosmetic product in the EU. Regulation (EC) No 1223/2009 contains in Annex IV a list of authorised colours for cosmetics.

What this implies in practice:

• Each dye must have a CI (Colour Index) number and be listed on the EU positive list
• Dyes labelled as „soap colorant“ or „for soap use only“ may not be approved for cosmetics - check CI number
• The documentation for the dye (SDS - Safety Data Sheet) must confirm the cosmetic use
• In the PIF (Product Information File) each dye must be listed with a CI number and proof of conformity

The most commonly allowed CI codes in CP soap:

Always buy dyes from suppliers who explicitly state "cosmetic grade“ and the relevant CI number.

How to add synthetic dyes correctly?

What is the easiest method?

Premixing in oil (recommended for mica and oxides)

Synthetic dyes are hydrophobic (or ambiphilic) - they disperse better in oil than in water.

Procedure:

1. Weigh out 1-2 tablespoons of neutral oil (sunflower, castor).
2. Pour the dye into the oil.
3. Rub with a spatula or disperse with a mini-mixer (pocket stick mixer or soap spatula) until a smooth, lump-free paste.
4. Add the paste to the light trace and stir in thoroughly.

Why this works: The oil prevents the pigment from clumping and ensures even colouring of the entire batch.

Are there alternative methods?

Premixing in water (for water-dispersed pigments)

Some specialty pigments are formulated as water dispersed - they are pre-mixed with glycerin or another carrier. These can be added directly to the trace or mixed with a small amount of distilled water.

Addition to the leaching solution (only for stable dyes)

Titanium dioxide and most oxides will survive the alkaline pH of lye - they can be dispersed in a small amount of oil and added before saponification. Do not use Ultramarine in lye - acidic traces in the leaching solution (even from water) can cause degradation.

Titanium Dioxide: white colour and opacity

What is titanium dioxide and what is it used for?

Titanium dioxide (TiO₂, CI 77891) is the most commonly used white pigment in soapmaking. It not only colours soap white - it adds opacity and a "clean&#8220look.

Dosage: 1 teaspoon per 500 g of oils for white. For full opacity (suitable for layered designs) increase to 2 tsp.

Warning - Turmeric and TiO₂: Turmeric (a natural dye) reacts with titanium dioxide to produce green or olive stains. Never combine these two pigments in the same section of soap. Use them separately in different layers or the design must physically separate the two colors.

Forms of TiO₂: Sold as a dry powder or pre-dispersed in glycerin/oil. The pre-dispersed version is more convenient (less dusting) but more expensive.

Summary table of synthetic dyes

*Ultramarine is stable in finished soap, but sensitive to acidic environments during manufacture - do not add to lye.

How to mix pigments for new colours

Can I mix oxides together?

Like paints, oxides can be mixed to achieve new shades:

• Red + yellow iron oxide → orange/terracotta
• Red + black → dark red-brown
• Blue ultramarine + white (TiO₂) → light blue, pastel
• Blue + red ultramarine → purple (unless you have directly purple oxide)
• Black + white → grey (different intensities depending on the ratio)

Tip: Always test mixing in a small amount of oil before adding to the whole batch. The resulting colour may be different to the paper - the alkaline environment of the soap may shift the shade.

The most common mistakes with micas and pigments

What are the most common errors?

Lumps in the soap: Cause - adding dry powder directly to the trace without pre-mixing in oil. Solution: always premix in oil.

Too light in color: The dosage was too low or the pigment was added too late (for a strong trace), when it did not disperse evenly. Increase the dose or add earlier.

Bleeding into the adjacent layer: The dye is prone to bleeding (especially neon micas). Solution: test beforehand, or use the dye only in single color soap.

The greying of the blue ultramarine: The soap was too warm or the acidic traces in the water reacted with the ultramarine. Store the soap in a cool place or use distilled water.

Frequently asked questions

Is mica safe in soap? Yes. Mica is a mineral compound that is not absorbed by the skin in topical use. The EU allows it in cosmetics. Always buy cosmetic grade mica, not industrial grade.

Can I combine natural and synthetic dyes? Yes, they are often combined. Natural dyes for earthy tones, synthetic oxides for intense colours. Test the combination - some dyes can react (like turmeric with TiO₂).

Why did my white soap with TiO₂ turn a little yellow after 4 weeks? Titanium dioxide is stable, but the very soap may turn slightly yellow over time due to oxidation of unsaponified oils. This is not the fault of the pigment. Add vitamins E or ROE to the recipe to slow down oxidation.

I do not buy dyes with CI numbers - what now? Contact the dealer and ask for CI number and confirmation of cosmetic use. If they cannot provide documentation, it is probably not cosmetic quality and you cannot sell it without risk.

Why do some dyes bleed and others don't? Bleeding depends on the nature of the pigment. Some pigments, especially neon micas and certain synthetic dyes, are mobile in alkaline soap and migrate to adjacent layers. Stable pigments (oxides, natural clays) do not move.

See also:

• Natural dyes for soap - organic alternative with lower stability
• Swirl techniques - how to use dyes for decorative effects
• EU regulation for manufacturers - Legislation for cosmetic dyes
• Troubleshooting color problems - solving specific faults