Caking:-
Settling of a dense deposit in a coating material that cannot be re-dispersed by simple stirring.

Catalyst
A substance that increases the rate of a chemical reaction, but remains chemically unchanged at the end of the reaction. The term is often wrongly used for materials that enter into the reaction e.g. hardeners or curing agents

Chalking :-
Formation of a friable powder on the surface of a coating giving a chalky appearance. Caused by disintegration of the binder by weathering (oxidation and or UV degradation) and release of the pigments and/or extenders at the surface. See 'Paint defects' in 'Helpline' for more information.

Checking:-
Crow's-foot or very fine wrinkling effects on surface or a fine wrinkle. See 'Paint defects' in 'Helpline' for more information.

Cissing:-
Small holes in the surface. Caused by oil grease or silicone contamination. See, fish eyes. Cratering See 'Paint defects' in 'Helpline' for more information.

Cloudiness:-
Lack of clarity or transparency in e.g. a binder solution, a solvent or a dried varnish film. (See opalescence)

Coating:-
A film forming material applied to a substrate to provide a decorative, protective or functional adherent film

Cohesion:-
Propensity of a single substance to adhere to itself; internal attraction of molecular particles towards each other. The forces that bind a coating film into a coherent whole. See Adhesion.

Colourant:-
Any substance that imparts colour to another substance tic can be dyes or pigments; concentrated pigment dispersion used to tint paints to a desired colour

Compatibility:-
Ability of two or substances to form a stable homogeneous mixture when mixed with each other.

Consistency:-
A general term for the property of a material whereby it resists permanent change of shape

Contrast ratio:-
Ratio of the reflectance of a dry paint film, applied at a specified thickness over a black substrate, to the reflectance of a dry film of the same paint applied at the same film thickness over a white substrate.

Convertible:-
A coating whose binder undergoes a chemical change during drying. The change is not reversible, and the binder is no longer soluble in its original solvent.

Cosmetic corrosion:-
The type of corrosion that occurs on an automotive body when the steel substrate has been exposed as a result of adventitious mechanical damage.

Cratering:-
Small holes in the surface. Caused by oil grease or silicone contamination. See cissing, fish eyes. See 'Paint defects' in 'Helpline' for more information.

Cross-cut adhesion test:-
A simple test to evaluate the adhesion of a coating to a substrate.