Flaking is the lifting of small-to-large sections of the paint and is due to poor adhesion and to the brittleness of the paint. The causes can be varied, for example the defect could be caused by efflorescence or the migration of soluble salts to the paint-media interface which can cause the paint to be forced off the surface. The paint may react with moisture and any traces of alkali to decompose the paint - this is called saponification. It may be due to failure to remove millscale from the steel before painting.
The removal (chipping away) of emulsion particles from the edges of the film that tend to redeposit in the image area while the film is going through the projector gate. Flaking is cased by a lack of proper edgewax lubrication.