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C1h) Paints and Pigments
PIGMENT: Gives the paint it's colour
BINDING MEDIUM: Sticks the pigment in the paint to the surface
SOLVENT: Dissolves the binding medium and makes it more fluid.
Why do we use paints: To look attractive and for protection (rust, woodwork against rain)
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.
The pigment is not dissolved in the binding medium and solvent forms a colloid
OIL PAINTS: Once it has been painted onto a surface:
The solvent evaporates
The binding medium dries forming a skin
The skin sticks the pigment to the surface
The oil is oxidised by atmospheric oxygen
The evaporating solvent is a pollutant
EMULSION PAINTS: water based paint contains small amount of oil.
Oil does not mix with water forms oil droplets spread throughout the water
Tiny droplets of one liquid in another liquid are called Emulsion.
Painted onto surface:
The droplets of oil join together to make a continuous film
Skin sticks the pigment to the surface
Emulsion paints contain less solvent than oil paints
THERMOCHROMIC PIGMENTS: Sensitive to temperature. Hot change colour, Cool change
to original colour. Cups, electric kettles (boiling water), toys (warn if it is too hot for baby).
Come in a limited range of colours so: they mix with different colours of acrylic
PHOSPHORESCENT PIGMENTS: Glow in the dark because they absorb radiation and store
energy and release the energy as light over a period of time.
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.
In the past, glow-in-the-dark watch faces used radioactive paints. Phosphorescent pigments are
much safer, though.