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Paint as a colloid

Paints are a type of mixture called a colloid. In a colloid, particles of one substance are mixed and dispersed with particles of another substance - but they are not dissolved in it. The components do not separate out because their particles are small enough not to settle at the bottom.

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Paint dry

Paint dries as the solvent evapourates.

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Thermochromic paints

Thermochromic pigments are sensitive to temperature. They change colour when they are heated up or cooled down. This property is useful for indicating if the drink in a cup is hot, or if the water in a kettle is hot.

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Phosphorescent paints

Phosphorescent pigments glow in the dark. They are able to absorb light energy and store it. This stored energy is released as light energy over a period of time.

Phosphorescent pigments are useful for watching faces that glow in the dark. They may also be used in fire safety signs placed near fire extinguishers. In the event of a fire, the location of the fire extinguishers can be seen even if the lights fail.

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How oil paints dry

The pigments in oil paints are dispersed in oil, which may itself be dissolved in a solvent.

The solvent evaporates away when the paint dries. This leaves the pigment and oil behind. The oil oxidises to form a hard film. This happens because the oil reacts with oxygen in the air.

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Safer than radioactive

In the past, glow-in-the-dark watch faces used radioactive paints. Phosphorescent pigments are much safer, though.

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