Mica and pearlescent pigments: particle size decides everything you see

Mica CI 77019 and synthetic fluorphlogopite compared on particle size from 5 to 150 microns, the coating that creates colour, lip approval and the sourcing question.

A pearlescent pigment is a layered optical device rather than a coloured powder, and almost every complaint about one traces back to a number nobody asked the supplier for: particle size. This page covers what is in the jar, how the coating makes colour, why "cosmetic grade" settles nothing about lip use, and what a sourcing claim must rest on.

• INCI: Mica (CI 77019)
• Satin 5-25 microns
• Sparkle 100-150 microns
• Use 0.5-6%
• Cosmetic grade is not lip grade

What is actually in the jar

Uncoated mica is nearly useless as an effect pigment. It is a transparent aluminosilicate that cleaves into thin flat sheets, with a refractive index around 1.58, close enough to an oil's that light passes through with only a faint whitish scatter. Everything you see in a commercial pearl was deposited on that surface.

The construction has three parts. A transparent platy substrate provides two parallel flat surfaces. A high refractive index coating, usually titanium dioxide at 2.5 to 2.7, sometimes iron oxide at around 3.0, is precipitated onto it by controlled hydrolysis of a metal salt and calcined, so light reflects both at the top of the coating and at the coating-substrate boundary and the two reflections interfere. Many pigments add a third part, an ordinary absorption colourant blended in to reach a target shade, and that is where most of the regulatory trouble lives.

Geometry does the rest. A mica flake is 0.3 to 0.5 microns thick and 5 to 150 microns across, an aspect ratio between about twenty and three hundred. Flakes that flat lie parallel in a setting balm and reflect in the same direction at once, which is what makes a pearl look like a mirror rather than a haze. Break them and you lose the effect.

Natural mica against synthetic fluorphlogopite

Two substrates dominate. Natural muscovite mica is mined, ground, sieved and classified. Synthetic fluorphlogopite is grown from a melt of magnesium, aluminium, silicon, potassium and fluorine compounds in a furnace at well over 1,000 C, then delaminated.

The performance difference is real but smaller than the marketing suggests. Fluorphlogopite is purer and more uniform in platelet thickness, so its interference colour is less diluted by scatter and reads brighter, particularly in blues and greens. It costs more. Natural mica gives a warmer, softer pearl that many people prefer on skin.

The label difference is sharper. Mica is a listed colour additive and carries CI 77019 on an ingredient list. Synthetic fluorphlogopite is not a listed colourant anywhere, so it appears under its INCI name as an ordinary ingredient and the colour is attributed to the coating, typically CI 77891. Put that to a supplier in writing before building a lip product on it: the substrate's permitted use is a separate question from the coating's. The general framework is in colourants and tints.

Particle size decides everything you see

Two pigments with identical chemistry and different particle sizes make completely different products. Larger platelets reflect more per flake and there are fewer of them, giving discrete bright points and little hiding power. Smaller ones pack densely into a smooth sheen with better coverage and no sparkle. No size does both.

Lips and tongue register discrete particles from roughly 20 to 30 microns upward, the threshold that makes coarse fat crystals perceptible in grainy shea butter, and above about 50 microns a lip product reads as textured whatever else is right. Because it is the largest particles you feel, ask for the top cut, D90 or D98, not the median.

How the coating makes the colour

Interference colour comes from the optical thickness of the coating, its refractive index multiplied by its physical thickness. The two reflected beams travel different distances, so one band of wavelengths is reinforced in reflection and its complement dominates in transmission. Because titanium dioxide's refractive index is high, a few tens of nanometres moves the reflected colour right across the spectrum.

Two consequences catch people out. Interference colour changes with viewing angle, which is what a duochrome pigment is and why a swatch photographed straight on is not what a customer sees in a mirror. And it has no hiding power, so it only shows against a contrasting background: a blue interference mica in a clear lip balm reads as faint grey shimmer, because there is nothing dark behind it. Visible colour needs an absorption pigment underneath, the job of iron oxides and mineral pigments, and what a lip film does to reflected light is in lip colour and gloss physics.

Iron oxide coated micas are more forgiving, because iron oxide absorbs as well as reflects, so bronzes and coppers hold over a pale base where a titanium dioxide pearl washes out. They carry CI 77491 alongside CI 77019. Ask one further question: whether the titanium dioxide is rutile and carries a silica or alumina passivation layer. Anatase is markedly more photocatalytic, and here it sits at the surface in contact with the oil phase, so an unpassivated grade can accelerate the process in rancidity and oxidation.

Cosmetic grade is not lip grade

Colour additives are governed by positive lists. US cosmetic listings sit in 21 CFR Part 73, Subpart C, where many entries are restricted to externally applied cosmetics, a phrase that excludes lips because a lip product is partly ingested. In the EU and UK, Annex IV of Regulation (EC) No 1223/2009 carries a field of application column, and a lip balm contacts mucous membrane, the strictest band. Mica, titanium dioxide and iron oxides are generally permitted for lip use in both. That does not make a given jar of pearl permitted, because the finished pigment is a mixture and its status is the intersection of everything in it.

A usable supplier statement contains all five of these. Anything less is a shop assurance, not evidence.

1. Full composition. Every component with INCI name and CI number: substrate, each coating layer, and every blended colourant. Not a shade name.
2. A named permission. A statement identifying the market and the instrument: all components permitted for lip use under 21 CFR Part 73, or compliance with Annex IV of Regulation (EC) No 1223/2009 including products applied to the mucous membranes. A bare "lip safe" identifies nothing.
3. Heavy metals with limits and method. Lead, arsenic, mercury, cadmium and antimony, with numerical limits and a batch certificate of analysis. Mined pigments carry these traces, and lip products swallow a fraction of what is applied.
4. Substrate identity. Natural mica or synthetic fluorphlogopite, stated explicitly.
5. Particle size distribution. D50 and D90 from laser diffraction.

What else is blended into a craft mica

Pigments sold under a shade name are frequently mica and titanium dioxide plus one or more of: iron oxides, carmine (CI 75470), ultramarines (CI 77007), manganese violet (CI 77742), chromium oxide green (CI 77288), ferric ferrocyanide (CI 77510), tin oxide and certified organic lakes. Four consequences follow.

Lip status. Ultramarines, chromium oxide greens and ferric ferrocyanide are listed in the US for externally applied cosmetics only, and those three are how most blue, green and violet shades are reached. Assume a craft mica in those colours is not for lips until the supplier proves otherwise.

Vegan claims. Carmine is made from cochineal insects, and a shimmer described only by shade name can carry it. A lip balm marketed as vegan with a carmine-containing pigment in it is making a false claim, with the consequences in vegan and cruelty free labels.

The ingredient list. A shade name is not an ingredient. The pigment must be decomposed into its components and each declared, colourants at the end of the list, by CI number in the EU and UK. The "may contain" or "+/-" convention exists for a product sold in several shades, not as a way of avoiding knowing what is in one. The INCI list builder handles the ordering, and what a reader can infer from the result is in reading a balm label.

Lightfastness. Mineral components do not fade, organic lakes blended into a shade do, so a pigment can drift on a sunny shelf while the mica in it does not.

Use levels, and why you must not grind it

Mica is dispersed, not ground, and this is where most people ruin an expensive pigment. Iron oxides arrive as agglomerates needing real shear, so the standard advice is to mull them into castor oil on a tile. Apply that to a pearl and you fracture the platelets, cutting the aspect ratio that produces the reflection. Hard-mulled mica comes out visibly duller and greyer, and prolonged high-shear mixing does the same more slowly.

1. Slurry rather than mull. Fold the pigment into warm castor oil with a spatula, roughly one part pigment to two or three parts oil, until uniformly wet. Castor oil is the right carrier for the reason in castor oil: ricinoleic acid's hydroxyl group makes it unusually polar, so it wets a mineral surface and displaces air.
2. Check for clumps, not for grit. Draw the slurry thinly across glass and look for dry agglomerates and dull patches. The platelets are meant to be there, so slight texture is not a fault.
3. Add late and stir gently. Stir it into the melt once the wax is fully liquid, at the cool end of the melt rather than at 80 C, and keep the batch moving.
4. Judge on a set swatch. Molten balm hides sparkle almost completely, and pearl reads differently under shop lighting than a workshop bulb.

Streaking has three causes needing different fixes. Dry pigment tipped into a melt never fully wets, leaving bright specks against dull ground. Platelets align with the flow, so balm poured slowly down one wall of a tube sets banded and directional, which is why you pour quickly and down the centre. And the pigment settles, which is the next section. Diagnosis by symptom is in streaky or mottled colour.

Settling, and the pour temperature that prevents it

Mica has a density around 2.7 to 2.9 g/cm3 against roughly 0.86 for molten balm. That difference drives settling, and Stokes' law makes the rate scale with the square of particle diameter, so size decides this too.

A lip tube column is around 55 mm, so a 100 micron sparkle can migrate a third of its length in the minute a hot batch takes to set, while a 15 micron satin grade barely moves. That is why coarse shimmer separates and fine sheen does not, and why the answer is rarely "stir harder".

The lever is viscosity, which rises steeply as the wax network forms. Pour at the cool end of the window rather than the middle: 65 to 68 C for a lip tube rather than 70 to 72, and 60 to 63 C for a tin, within the ranges in pour temperatures. Stir until the batch just begins to cloud, pour immediately, and cool the filled tray promptly rather than letting it stand warm. A carnauba formula is the awkward case, because it must be poured near the top of its window to avoid lumps, so there you compensate with a finer pigment. Settling already done shows as a pale top and dense base in a tin, or a stick dull where it is first used and glittery at the bottom, and is diagnosed in pigment sinking to the bottom.

Where the mica came from

Mica is the one pigment on a balm bench with a serious human rights problem attached, worth stating plainly rather than ignoring or dramatising. A substantial share of world supply, commonly estimated at around a quarter, comes from India and Madagascar, much of it from small-scale, informal and often illegal mining. Child labour in that collection is documented by non-governmental field investigations, which put the number of children involved in the Jharkhand and Bihar mica belt at roughly 20,000 and in Madagascar at around 10,000. Those are survey estimates from a sector with no reliable register, so read them as orders of magnitude.

The Responsible Mica Initiative, formed in 2017, is the main industry coalition working towards a traceable and child-labour-free Indian supply chain, and publishes workplace standards and progress reporting. Membership is a company commitment, not an audit of the batch in your hand, and conflating the two is the commonest overstatement in this area.

A responsible sourcing claim needs four things behind it: a named country and region of origin, documented chain of custody from mine through processor and pigment manufacturer to you, third-party verification rather than self-declaration, and evidence attached to the batch you bought. Most small makers buy repacked pigment from a reseller and can obtain none of it, so say what you actually know. "Our supplier is a member of the Responsible Mica Initiative" is defensible if true and documented; "ethically sourced mica" with nothing behind it is the sort of unsubstantiated claim discussed in chemical free and clean beauty claims, and in the UK and EU it faces the same fairness rules as any other product claim. The questions to ask are in sourcing ingredients.

Synthetic fluorphlogopite removes the mining question for the substrate, a genuine answer to a labour problem though not an environmental one: it is grown in high-temperature furnaces at real energy cost, and the coating precursors are mined regardless.

What mica cannot do for you

It adds shimmer, not colour: a pearl over a colourless base is a colourless pearl, and no amount of it makes a tinted product. It does nothing for skin, being purely an optical additive with no conditioning or barrier function. It makes an already draggy balm worse, because hard platelets between film and lip are an abrasive, the mechanism in drag and poor glide, so fix the glide before adding sparkle. And weighing loose fine powder is a respiratory exposure worth a mask and a still bench, though the pigment is harmless once bound in oil.

The decision order is what most people get wrong. Choose particle size first, from the feel the product must have, because that constraint is absolute for a lip product and nothing later rescues it. Choose the coating second, for the colour and the base it sits on. Confirm the lip status of every component third, in writing, before buying in quantity. Decide the substrate last, on cost and on what you are prepared to say about sourcing. In that order a shimmer balm is straightforward, as in tinted lip balm. In reverse you end up with a beautiful pigment you cannot legally sell.

Reviewed and updated 6 September 2026. Spotted an error? Tell us and we will fix and log it.