Benard (Vortex) Cell
n Hexagon-shaped cell that is produced by the vortex action of solvent evaporation in thin films. During drying, all solvent paints and many varnishes exhibit Benard cell formation, i.e., roughly hexagonal cells, generally with a well-marked center. The whole cell is in movement with currents streaming up the center and flowing down the walls. These current, because they affect pigments differently, lead to segregation and deposition of different components in different parts of the film. This phenomenon manifests itself in color and surface irregularities of the film. (Weldon DG (2001) Failure analysis of paints and coatings. Wiley, New York).