Watching Paint Dry

When colloids like paint dry, they can form microscopic zigzag patterns thanks to shear stress from evaporating water molecules.
When colloids — suspensions of particles in a fluid — dry, they can form regularly-spaced zigzagging bands. Now, scientists think they know why.

August 20, 2015

The pattern you see above, referred to in technical terms as a chevron, occurs naturally when the water in a thin colloid film (like paint) evaporates. Because one side of the paint is drier than the other, water molecules migrate toward the dry side, carrying pigment particles with them. This effect creates shear stress in the transition zone between wet and dry, forcing the solid into this corrugated structure. In this picture, the film dried from bottom to top.