Expression, in reference to a painted surface, indicates a stretching defect of the paint, generally due to an inadequate dilutent, a too high viscosity of the painted object or a too high or too low temperature for the environment. In restoration, it indicates, in the same way, the aspect assumed by a pictorial surface caused by the harmful effect of a heat source (see blister). An incorrect ironing during the lining of a painting may equally provoke the phenomenon.