Correct Answer - Option 4 : White lead
Concept:
Paints:
It is the mechanical dispersion of one or more fine pigments in a medium (thinner + vehicle). When the paint is applied to a metal surface, the thinner evaporates, while the vehicle undergoes slow oxidation leading to the formation of a pigmented film.
Constituents of paint:
1. Base:
It is a metallic oxide which is the principal constituent of a paint. It makes the paint film opaque & processes binding properties which reduce the shrinkage cracks in the film on drying.
E.g- White lead, Red lead, Zinc oxide, Iron oxide, etc
2. Vehicle or drying oils:
It is a liquid that binds the pigment to the surface and protects pigment from decay e.g. linseed oil, dehydrated castor oil, etc.
E.g- Linseed oil, Tung oil, Poppy oil, Nut oil, etc
3. Extenders or fillers:
The function of the addition of filler in paint is that it improves the properties of the paint and mainly reduces the cost. The main purpose is to increase pigment volume concentration.
E.g- Gypsum, Calcium carbonate, Aluminium silicate, Magnesium silicate, Talc, Diatomite, etc
4. Thinners or solvents:
It is a volatile solvent, which is often added to paint which helps to adjust the consistency of the paint.
Solvents of oil paints are used to thin the paints and increase the spread.
E.g- Turpentine, White spirit, Naptha, Benzine, Petroleum, etc
5. Drier:
The main function of a drier is to increase the drying power of the vehicle. They act as oxygen-carrying catalysts.
E.g- Litharge, Red lead, Sulphate of manganese, etc
6. Plasticizer:
They remain permanently in paints and varnishes. They improve the elasticity of the paint film which prevents cracking of the film.
