Definition - What does Mottle mean?

Mottle is a coating defect characterized by a ring-like blotch with a light-colored area in the center of the ring. Mottle typically occurs when metallic flake pigment is used in a coating.

It typically appears as a mark with spots or blotches of different color or shades, as if stained.

Corrosionpedia explains Mottle

Mottling is a dull, hazy or blotchy appearance on the surface of vinyl films or over laminates. It is an undesirable defect which can occur with effect coatings, most obviously on light metallic finishes. The total color impression shows irregular areas of lightness variations. The mottled look can be subtle, with different hues of the base color being applied to add depth and giving color a variation in intensity and shading. It can be caused by the coating formulation, as well as variations in the application process.

For example, disorientation of the metallic flakes or film thickness variations of the base coat can lead to various mottle sizes resulting in a non-uniform appearance. The visual perception of mottling is dependent on the viewing distance: large mottles can be seen from a distance, while small mottles are more noticeable close up. Visual evaluation of mottling is very subjective, as it depends on the illumination conditions, observing distance and viewing angle.

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