Thermochromic (temperature-sensitive) and photochromic (light-sensitive) nail polishes are also possible. Thickeners, such as stearalkonium hectorite, are added to keep pigments and other additives suspended in the polish. Pearlescence can be achieved through the use of finely ground titanium dioxide or mica mixed in with the nail polish, and small pieces of glitter can also be included. More complex coloured effects are also possible. Organic pigments are similar to those used in food colourings, and come in a range of colours. Inorganic pigments used include chromium oxide for greens, iron oxide for reds and oranges, and ferric ferrocyanide for blues. These tend to be pigments, either inorganic or organic (carbon-based). The key ingredients in nail polishes are the compounds that give them their colours. The latter, increasingly used as a replacement for DBP, has also been linked to concerns regarding hormone disruption, showing that finding safe replacements for banned ingredients in cosmetics is not always easy. It has also been phased out in the US, and other plasticisers have taken its place, including camphor, glyceryl tribenzoate, and triphenylphosphate (TPPP). Dibutyl phthalate (DBP) was a widely used plasticiser but its use has been banned in the EU since 2004 due to concerns over the possibility of of it interfering with the human hormone system. The plasticisers used in nail polishes are not without a degree of controversy. They remain behind when the solvents evaporate or when the polish is cured with UV light in fact they are used in a wide range of plastics, not just polishes, and help to add flexibility. These are compounds added to stop the polish from easily cracking or chipping. In both conventional and gel nail polishes, plasticisers are also used. There’s a good more detailed explanation of how this happens here, as well as an explanation for a particular example in this article by Tom Husband. Instead they are applied in layers which are exposed to ultraviolet light this kicks off a polymerisation process which solidifies the polish.
Unlike conventional nail polish, these mixtures aren’t simply applied and left to dry. Gel nail polish is an alternative formulation which consists of methacrylate compounds and photoinitiating compounds such as benzoyl peroxide. This conventional nail polish is not the only option, however. These so-called film modifiers also impart a glossiness to the polymer finish. Adhesive polymer resins that are also contained within the formulation help the polymer film to stick to the nail. When it is applied the solvent evaporates, leaving the polymer to form a film on the nail. In this graphic and article, we take a look at the different chemistry that comes together to colour your nails.Ĭonventional nail polish consists of a polymer, most commonly nitrocellulose, dissolved in a solvent, usually ethyl acetate or butyl acetate. Polymerisation, thixotropic agents, solvents and thermochromism are all terms you might expect to hear more frequently in a lab than in a nail salon, but they can all crop up in relation to nail polish. Painting your nails with nail polish might not seem like a particularly complex chemical process, but there’s much more to it than meets the eye.
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