Interaction between canvas and paint film in response to environmental changes

Abstract

Using a biaxial stress tester for stretched canvas, a canvas sample carrying a heavy paint film has been tested for changes in tension caused by fluctuations in temperature and relative humidity (RH). The paint and priming were then removed and the bare, sized canvas was exposed to the same fluctuations in temperature and RH as before. These tests provided first-hand measurements of the tension within the canvas and paint layer and of the shear forces between these layers. A comparison of results demonstrates that cracking and deterioration is caused primarily by the paint film, which deforms the canvas and generates stress, rather than by movements of the substrate, as previously believed. This experiment provided additional proof for earlier fundamental findings (that small temperature changes have a considerable effect on the stress in the tested samples and, therefore, on canvas paintings and other surfaces). This study also provided more evidence that high RH (above 90%) can be extremely dangerous for the preservation of canvas paintings, but does not imply that smaller changes in RH may not be damaging to the structure of a painting.