Abstract: A method includes steps for modifying tensile stresses in an unpainted canvas that is mounted on a frame under applied tensile stresses. The canvas is formed of material that can undergo heat-shrinking when at or above a thermoplastic shrinking temperature, and can undergo heat-softening when at or above a thermoplastic softening temperature. The method includes heating the canvas to a temperature at or above the thermoplastic shrinking temperature and the thermoplastic softening temperature. The method further includes maintaining the canvas at a temperature at or above the thermoplastic shrinking and softening temperatures. This induces heat-shrinking, and thereby increases the tensile stresses in any portions of the canvas in which the applied tensile stresses are less than the opposing stresses of the heat-shrinking.