Paints and Pigments
- Pigment - gives the paint its colour
- Binding medium - liquid that carries the pigment bites and holds them together. When it turns to solid, it sticks the pigments to the surface you've painted.
- Solvent - keeps the binding medium and the pigment runny - as a liquid in a tin or paste in a tube.
Paints are colloids:- a colloid consists of really small particles of one kind dispersed into a another kind.
The particles can be bits of solid, droplets of liquid or bubbles of gas.
Colloids don't separate because the particles are so small.
Emulsion paints > water based. The solvent is water, binding medium is a polymer such as acrylic.
Gloss paints > oil based. Binding material is oil, the solvent is an organic compound such as turpentine.
Paints and Pigments
Some solvents in oil based paints produce fumes that can be harmful so there has to be plenty of ventilation.
Water based emulsion > solvent evaporates leaving behind the binder and pigment. It dries quite quickly.
Oil based > take longer to dry because the oil has to be oxidised by oxygen in the air before it turns solid.
To paint the outside part of a door:
- Hard wearing
- So it would be oil-based gloss.
To paint bedroom walls:
- Goes on easily
- Dries quickly
- Doesn't produce harmful fumes
- So it would be water-based emulsion
Dyes and Special Pigments
- Used to colour fabrics
- Originally, people made dyes from plants by grinding the plant with water or another solvent and draining the liquid. Example, indigo dye comes from a plant.
- Over the past hundred years, people have invented a lot of synthetic dyes.
- Change colour or become transparent when heated or cooled.
- Different pigments change colour at different temperature.
- Used in novelty drinking mugs, safety signs, clothing.
- Glow in the dark.
- Absorb light/artificial light and store the energy in molecules. This energy is released as light over a period of time.
- Used in clocks, novelty decorations.
Aluminium and Iron are extracted from ores in rocks.