Pigments are the third component of our paint systems. They fall into two main groups, prime pigments and extenders, with two smaller groups of metallic and pearlescent, of particular importance to the motor car business. Prime pigment is an essential part of all coloured surface coatings both in undercoat and topcoat. It is the material, organic or inorganic, that gives the characteristic colour, which may be used singly, or as a mixture of pigments. Extenders are inorganic materials of mineral origin, chalks, talcs and china clays are examples. They are greyish white colour when seen in the dry state, but become translucent when wetted in dispersion, therefore not affecting the colour of the prime pigment. In undercoats they provide the dry film properties such as filling (by the nature of their bulk) and sanding (due to their friable nature). In topcoats they may be used for creating semi-gloss or matt finishes. More importantly, they can be used to extend the volume of the heavier coloured pigments, as well as preventing hard settlement. Metallic pigments - there may be two types of metallic used: 1) Aluminum flakes produced by-milling the metal to produce small platelets in various grades, from very fine to very coarse. They are supplied in the form of a paste for ease of handling and to reduce the fire risk. When used in vehicle finishes, they are combined with the more transparent organic coloured pigments, so as to retain the sparkle. Aluminum flakes are also used in primer sealers where the platelets form a barrier to seal off underlying coatings, such as Bituminens. 2) Zinc flakes are used in zinc rich coatings, either to inhibit corrosion of metal or to allow welding through primer and prevent joint corrosion. Pearlescent pigments - these originally consisted of fish (Bleak fish) scales, which gave the effect of artificial pearl and were used in the glamour and trinket trade. Technology now produces pearl effects using prismatic mica particles, which can be designed to bend the light and may be coated with metal compounds to give various effects. Paint is made by mixing pigment with a vehicle, but simple hand stirring will not give the necessary degree of dispersion. The heavier action of squeezing or rubbing is necessary if the pigment is to be thoroughly distributed or dispersed and ‘wetted’ by the vehicle.