Why Is Milk White?: & 200 Other Curious Chemistry Questions (2013)
How do people make different nail polish colors?
Since nail polish is a cosmetic, the pigments and dyes are selected from the list of D&C colors regulated by governments. These colors were discussed earlier in the question about the colors in shampoo (page 31).
The pigments in nail polish are generally dissolved with a filmforming plastic in a solvent. A typical film-forming plastic used is the explosive nitrocellulose, one of the ingredients in smokeless gunpowder. This is dissolved in a relatively safe solvent, such as ethyl acetate or butyl acetate (or both) and sometimes isopropanol.
To make the colors opaque, pigments such as titanium dioxide may be added. Thickeners such as stearalkonium bentonite (a type of clay) are also added. To get pearlescent effects, flakes of fish scales, tiny flakes of aluminum, or even minute flakes of stainless steel can be added. These give metallic sheen to the nail polish. Platelets of mica can also be used to give a shiny effect.