Revision OCR Chemistry 2+3 (higher tier)

C2a Paints and pigments

·         Synthetic dyes introduced a wider variety of colours and are now mainly used

·         Paints contain coloured pigments, a solvent and a binding medium.  The solvent thins it while the binding medium hardens when exposed to oxygen

·         Paint is a mixture, a colloid – solid particles mixed with liquid particles (solvent).

·         The solvent evaporates leaving the colouring, which is no longer a liquid

·         In emulsion (water-based) paints, the solvent is water; a polymer is used as the binding medium.  The solvent evaporates, the polymer particles fuse into a film

·         Oil paints use hydrocarbon oil as the solvent, when it evaporates the binding medium oxidises to form the film

·         Gloss paints used to be made from a hardening oil but it took several days to dry

·         In modern gloss paints the alkyd resin (binding medium) is a polymer

·         Some paints contain thermochrmoic pigments which change colour with heat

·         Others contain phosphorescent pigments, which make it glow in the dark