Duochrome is a nail polish finish that uses interference pigments which shift between two colours as the viewing angle changes, for example green to purple, with the strongest shift over a black base.
Also known as: duochrome polish, two-tone shift polish, colour shift polish, duo chrome
Duochrome polish contains interference pigments: flakes of mica or borosilicate coated with thin layers of titanium dioxide or iron oxide. The coating reflects one colour straight on and another at an angle. A classic pairing is green to purple, or blue to pink. The shift is a physical effect of the coating, the same effect seen on a soap bubble or a beetle shell.
Duochrome and multichrome share the same chemistry and differ in the number of colours. A duochrome shifts between two, a multichrome between three or more. Both look strongest over a black base, which absorbs the light that passes through the flakes and leaves only the reflected colours visible (Cirque Colors).
Duochrome differs from holographic. A holo splits light into the full rainbow through diffraction, always in the same order (Lab Muffin). A duochrome reflects two chosen colours through interference. The two effects can be mixed in one bottle, but they are separate pigments.
Duochromes come as opaque polishes and as sheer toppers. The topper form is the more common, because a sheer duochrome over a crème gives the strongest colour flip. Two thin coats, a glossy top coat and a dark undercoat give the clearest shift. The pigment family is the same one used in pearl and aura effects, and Cirque Colors sells it under its Shimmergraphic and Spotlight Shimmer lines.