Ingredients of paint and their role

Paint is a mixture of a base, vehicle, pigment, drier, thinner and sometimes extenders, in liquid form. When applied, the thinner evaporates, the vehicle dries and a hard coloured film remains.

1. Base: The main solid that forms the body of the paint and gives opacity. It fills pores and gives a uniform surface. Examples: white lead, zinc white, titanium white, red lead, iron oxide, aluminium powder.
2. Vehicle (carrier): A liquid, usually a drying oil (linseed, tung, poppy oil) that holds the base and pigment, spreads them and binds them to the surface on drying. It forms the tough film and gives durability and gloss.
3. Pigment: A fine colouring powder that gives the colour and also helps resist weathering (e.g. lamp black, chrome yellow, Prussian blue, red oxide, ultramarine). It also gives some opacity.
4. Drier: Added (about 8% by weight of oil) to speed up oxidation and hardening of the oil. Examples: litharge, red lead, manganese dioxide, cobalt compounds.
5. Thinner (solvent): Added to make the paint thin enough to spread and to dissolve the vehicle; it evaporates after application. Examples: turpentine, mineral spirit, naphtha.
6. Extender/adulterant (optional): Cheap inert filler such as barytes, gypsum, china clay, which adds bulk and reduces cost.

Ready mixed paint contains all of these in a can and needs only stirring and thinning before use.