Nitrocellulose is a cellulose-based film former that gives classic solvent nail polish its hard, glossy coating, forming a continuous film on the nail as the butyl and ethyl acetate solvents evaporate.
Also known as: cellulose nitrate, nitrocellulose nail polish, nitrocellulose lacquer
Nitrocellulose is the ingredient that makes conventional nail polish a polish. It is dissolved in volatile solvents, mainly butyl acetate and ethyl acetate, together with plasticisers, resins for adhesion and gloss, pigments and suspending agents. When the brush leaves a wet coat on the nail, the solvents evaporate and the nitrocellulose is left behind as a solid film (Personal Care Magazine).
A solvent polish dries from the bottom up, which is why a thin coat sets evenly and a thick coat stays soft underneath a dry skin. Regular polish is touch-dry in about 3 to 5 minutes and takes several hours to reach full hardness (Nagelstudios.nl). The nitrocellulose film is hard and bright on its own, so plasticisers such as citrates are added to keep it flexible enough to bend with the nail.
On an ingredient list the name appears as nitrocellulose, usually near the top because it is one of the largest components after the solvents. Every crème, jelly, shimmer and magnetic lacquer from India Anaïs is built on this system, which is why it needs no lamp and comes off with ordinary remover.
The alternative is water-based polish, which replaces nitrocellulose with an acrylic polymer dispersed in water. That system has no flammable solvents but dries more slowly and has historically worn less well (Personal Care Magazine). Gel polish uses a different chemistry again: acrylate monomers that cure under a lamp.