The use of a coating additive prevents small bowl shaped depression formed in the coating film. Having a low surface tension will produce a surface gradient to pull the coating away from pollutants, forming a bowl shaped depression around the raised rim.

Therefore, the coating leaves a small roughly circular pit - like a crater if the central pollutant is invisible, or "fish eye" if the central area is visible.

As the coating pulled away from the pollutants and began to lose the solvent, the viscosity was high and could not flow out, resulting in a crater thickened by the rim.

Craters are usually 1-3 mm in diameter. Craters are not always caused by internal coatings or contaminants on the substrate.

Common airborne particles will cause shrinkage on a wet surface in contact with a new coating. Some coatings tend to wait for these surface defects more easily.

Such low molecular weight resins are prone to occur and cannot be dried quickly. Defoamers and wetting agents for coatings may also cause surface defects.

Painting surface energy gradient caused by related phenomena of picture framing, Bernal cell formation, orange peel, edge pull and picture frame.

In general, the coating caused by this defect will flow from the area of low surface energy to the area of (relatively) high surface energy.

A variety of surfactants can alleviate or eliminate this problem, but fluorosurfactants are particularly effective in many cases.