Did you know that paints and adhesives contain plastics? Paints are often made of three different chemicals. A ‘pigment’ provides the colour; a plastic holds the pigment in place and gives a shiny finish; and a ‘solvent’, usually white spirit, makes the paint runny and easy to use. When the paint dries, the solvent evaporates and only the pigment and plastic are left.
Pigments
The pigment is the color chemical in paint. It looks a certain color because it reflects some wavelengths of light and absorbs others. Traditionally, metal compounds (salts) are used to create different colors so, for example, titanium dioxide (bright white chemical often found in sand) is used to make white paint, iron oxide makes yellow, red, brown, or orange paint and chromium oxide makes paint that’s green. Black comes from particles of carbon (think what your burned toast looks like and you’re getting close to a color chemical known as “carbon black”). Different pigments are mixed together to make paint of any color you can imagine.
Binders
Pigments are typically solids, so you couldn’t use them to paint by themselves. They’d be difficult to apply, they wouldn’t spread evenly, they wouldn’t stick to paper or a wall, and they’d wash straight off if they got wet. That’s why paints also contain substances called binders. Their job is to glue the pigment particles to one another, but also to make them stick to the surface you’re painting. Some binders are made from natural oils such as linseed oil, but most are now made from synthetic plastics. Visualize the binder as an invisible skin of plastic with a colorful pigment dispersed through it and you can see just how paint gives a layer of protection.
Solvents
Mix a pigment and a binder and you get a thick gloopy substance that’s difficult to spread. Ever tried painting a wall with treacle? That’s what using a pigment and a binder is like. It’s the reason why paints have a third major chemical component called the solvent. As its name suggests, a solvent is something that dissolves something else. The solvent’s job is to make the pigment and binder into a thinner and less viscous (more easily flowing) liquid that will spread evenly (that’s why paint solvents are sometimes called thinners). Once the paint has spread out, the solvent evaporates into the air, leaving the paint evenly applied and dry beneath it. When you apply a really nasty paint and there’s a smell lingering for days while it dries, that’s the solvent evaporating into the air.
Strong glues like ‘superglue’ are made of thermosetting plastics called epoxy resins. They can stick metal, glass, china, and wood— in fact almost anything!