| Pigments are fine powders that are spread throughout the paint film and help hide the surface underneath and may also provide colour. Paint is therefore a suspension (see Materials page 10) of pigment particles. The powder has to be insoluble in water, chemically un-reactive and should not fade in light.
Coloured pigments range from simple metal oxides such as red iron(III) oxide to complex organic molecules. Some examples of inorganic pigments are shown below.
| Colour |
Compound |
| Red |
Iron oxide |
| Cobalt blue |
Cobalt alumina hydrate |
| Green earth |
Iron oxide of aluminium silicate |
| Yellow |
Iron oxide hydrate |
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The most common white pigment is titanium dioxide. It is used because it is so opaque and scatters lots of light. Other white powders are much less opaque but are also added to emulsion paints because they have other desirable properties, such as helping one coat stick to the next one and preventing pigment particles settling to the bottom of the can. These compounds are called extenders.
The difference between a ‘matt’ and a ‘silk’ emulsion paint is the proportion of the courser extender particles they contain. Matt paint contains a greater proportion than silk paint does.
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