Pigment:-
A powdered insoluble solid, which provides optical properties such as, colour, reflectance, opacity. The term is also used in the coatings/ink industry for powders which, when dispersed in a liquid or solid binder, may also provide properties such as UV protection, corrosion inhibition or for modifying mechanical and flow properties.

Pin Holing:-
Small holes in film. Caused by moisture in airlines. Solvent trapped under film. See Solvent Popping, Cratering, cissing

Polymer:-
Materials whose molecular structure consists of one or structural units (monomers) repeated any number of times; a homopolymer has only one kind of structural unit which is repeated, while a copolymer has two or different structural units which are repeated.

Polymerisation:-
A chemical reaction in which two or small molecules (monomers) combine to form larger molecules (polymers) that contain repeating structural units of the original molecules.

Pre-treatment:-
The chemical modification of substrates in order to improve adhesion, provide an even surface for painting and in the case of metals, to provide some protection against corrosion. e.g. phosphating of steel

Primer:-
The first coat in a paint system, whose main function is to provide the adhesion between substrate and the total paint system. See also sealer, size, filler, bonding liquid, undercoat.

Primer Sealer:-
A coating material used to seal and simultaneously prime a suitably prepared substrate.

Putrefaction:-
The decomposition in the can resulting from bacterial attack on a coating material.

Reactive Diluent:-
A liquid which reduces the viscosity of a preparation but which takes part in the film-forming process by combining with one or of the constituents of a coating material.

Recoatability:-
The aptitude of a fully dried film of a coating material to accept, without adverse effect, a subsequent coat of the same or similar material.

Relative density:-
The ratio of the density of a material to the density of water at the same temperature. This is the preferred term in place of "specific gravity" or "SG"

Roller Application:-
A process whereby the coating material is applied by means of a hand-held roller of some soft material (e.g. foamed plastic, fabric or wool).

Runs:-
Running of wet paint into uneven rivulets. Cause - paint too thin. Solvents very slow. Very cold conditions. See Sags.