AIC's 41st Annual Meeting

Jia-Sun Tsang, Senior paintings Conservator, Don Williams, Senior Furniture Conservator, and Inês Madruga Carvalho Caldeira, paintings Conservation Fellow, Smithsonian Institution’s Museum Conservation Insitute (MCI); Rick Pelasara, Exhibit Production Manager, Smithsonian National Museum of the American Indian

Stretchers for paintings on canvas first appeared in the mid-18th century. Since then, a variety of devices have been used to expand the corners of stretchers to create tight, even surfaces. These devices have included traditional wooden wedges, modern ICA spring stretchers, and expansion bolt stretchers, all employed to impose dimensional changes at the corners. If not used properly, this type of expansion through corners can harm works of art by concentrating excess stress at corners, along with many other concomitant risks.

Previous MCI-based research ,2 into the mechanical behavior of paintings, combined with the authors’ experiential observations, provided the impetus to develop an innovative stretcher system that would provide strong, even, reliable support for a canvas without expanding the corners. We have developed a prototype stretcher made of aluminum and Delrin® (an engineered polymer with properties bridging the gap between metal and wood), with threaded thumb screws for tension adjustment positioned at calculated intervals along the stretcher bars, not at the corners. This system has several advantages: it can adjust the tension in each direction and location separately; it provides stability and even tension while conserving aged and lined paintings; and it effectively corrects planar distortions through infinitely variable localized tension adjustments.

This new system can be adapted to serve as an insert for retrofitting extant paintings with lax, nonplanar canvases that cannot be safely dismounted, and also as a new stretcher for original artworks. The prototype stretcher can be retrofitted to an existing painting to impart structural strength and integrity without imposing any new stresses or distortions on the extant stretcher corners. Instead, the stresses and concomitant strains are introduced along the bars of the stretcher, in effect allowing the corners to “float” and achieve their own structural equilibrium. This feature is even more pronounced in the prototype stretcher developed for new paintings, in that the intersections of the wooden tacking bars allow for the structural equilibrium required by the canvas. The use of this innovative system with modern and contemporary large-scale paintings has significant ramifications: besides providing structural soundness and even surfaces, adjustments and corrections of canvas tension can be made on-site in galleries and museums, without having to dismount the paintings.

As an example of this new stretcher’s practical application, to treat a 150-year-old painting with severe planar distortion and a fragile surface sensitive to moisture and heat, our team designed and installed a prototype as an insert. Fitting the at-risk painting with our newly designed stretcher immediately corrected the severe planar distortion of the canvas, without the use of heat, moisture, or weight.