In the main coating materials ready for use consist of film forming binding material (“resin”) and powder components such as the colour pigments, corrosion protecting pigments and fillers.

During weathering the aggressive ultra violet component of sunlight may damage the binding material so that after a time the pigments underneath are exposed to such an extent that the remaining material may come away as a result of simple contact or wiping. The effect on the exposed pigment when wiped is reminiscent of wiping chalk on a school blackboard.

In the established chalking test the exposed pigments are lifted off with a sticky substance after this has been pressed against the surface to be tested in a controlled manner.