Impasto is paint applied thickly enough to stand up from the surface, holding the shape of the brush, palette knife, or finger that placed it.
Identified by relief and shadow: an impasto passage casts its own small shadows across the surface and catches raking light differently from the flat areas around it. The thickness can be modest — visible ridges along the line of a stroke — or extreme, with paint built into sculptural lumps and crests. Impasto preserves the act of application unusually clearly, since the paint cools and dries in the form it was put down in; for that reason it tends to carry gesture vividly. The word is Italian, from impastare, to make into a paste. Often described in contrast with glazing, which is the smooth, transparent opposite.