Key takeaways
- Mica alone gives soft sheen; coated mica with titanium dioxide or iron oxide gives colour and sparkle.
- Particle size above 100 µm reads as glitter and tends to scatter across the face.
- Bismuth oxychloride gives strong lustre but is not suitable for every market.
Mica is a layered mineral that appears in almost every eyeshadow, highlighter and blush that shimmers. On its own it produces a soft sheen; coated with titanium dioxide or iron oxide it becomes a colour-shifting effect pigment with a specific size, shape and lustre. The particle size decides the visual result more than the colour does.
The category distinguishes three effects that marketing often conflates: sheen (fine, diffused, reads as skin glow), shimmer (medium, directional, reads as pearl), and glitter (large, individual sparkles that can travel across the face). Each maps to a particle size band, and each has a different wear behaviour on a lid.
1. Particle size bands
Below 15 microns the effect is a soft sheen. Between 15 and 40 microns the effect reads as pearl or shimmer with visible directionality. Above 60 microns individual flakes become visible as sparkle, and above 100 microns they read as glitter. A palette that mixes three sizes gives depth; a palette where every shade sits at 30 microns looks flat.
2. Coating and colour
Mica coated with titanium dioxide produces interference colours that shift with angle — the greens and pinks in a duochrome shade. Coated with iron oxide it produces warmer, more opaque tones. The coating thickness controls the colour, so two pigments from different suppliers at the same particle size can read differently.
3. Slip and pressability
Mica is platy and gives slip, which helps a powder spread. Too much mica makes a pressed pan fragile because the plates align and split; too little makes the powder drag. The usual balance is mica with a spherical filler such as boron nitride or a silica microsphere to break the alignment.
4. Fallout
Fallout — pigment landing under the eye — comes from large particles that do not adhere. A binder helps, and a slightly tacky base under the shadow helps more. Large-particle glitters will always fallout to some degree, which is why they are used as a topper rather than as a base shade.
5. Bismuth oxychloride and alternatives
Bismuth oxychloride gives a strong, almost metallic lustre and is common in high-end highlighters. It is also associated with irritation in a minority of users and is restricted in some markets. Synthetic fluorphlogopite is a mica alternative with a more consistent colour and no heavy metal concerns, at a higher price.
6. Regulatory and heavy metal checks
Mica is a mined mineral and can carry trace heavy metals, particularly lead and arsenic. Cosmetic grades are specified against a limit and tested per lot. A brand that switches to a cheaper mica supplier without checking the certificate is taking a compliance risk that will not show up until a market test.
7. Colour matching across lots
Effect pigments vary between lots more than flat pigments do, because the interference colour depends on coating thickness. A tolerance of 2 ΔE is realistic for shimmer shades, and a photograph under two light angles is more useful than a single spectrophotometer reading.
8. Pressing and pan performance
Effect pigments press differently from matte pigments: they need a lower pressure and a higher binder to stay intact. A pan pressed at the same force as a matte shade will crack along the plate alignment. The press parameters belong in the batch record alongside the formula.
9. Where it fits
Effect pigments appear across the eyeshadow palette range; the pressing question continues in the powder pressing entry.
Reference: Effect pigment supplier data and colour matching trials, 2025
