Frank J. Ligterink and Giovanna Di Pietro
A frequently observed phenomenon with canvas paintings is the sharp transition in the condition of canvas and paint layers in the regions directly adjacent to the stretcher, strainer or cross bars and the condition of the painting in the other regions, behind which no wood is present. This paper explores the idea that this transition, referred to as the 'stretcher effect', is the result of a local deviation of the relative humidity in the vicinity of the stretcher. Two plausible mechanisms, thermal shielding and hygroscopic buffering are investigated both theoretically and experimentally. It was found that thermal gradients cause significant variations in relative humidity near the canvas and thus play a major role in the formation of the stretcher effect.