The best paint effect is when the aluminum pigment is oriented parallel to the paint film. Bad parallel orientation can cause turbidity or diffuse reflection, and the evaporation of solvent can shrink the wet paint film and eventually press the aluminum pigment into a horizontally oriented position. The higher the solvent content, the more pronounced the orientation effect. So a low solids coating works better than a high solids coating. However, solvent evaporation will also cause strong eddy current inside the wet paint. If the solvent evaporates too slowly, the surface of the paint film is dry, and the internal solvent is still volatilized, which will cause voids on the surface of the paint film and affect the directional arrangement of the aluminum flakes. If this situation happened, add some additives to promote the orientation of the aluminum flakes.