When a museum decides whether to send a painting on tour, it relies on conservators to assess the fragility of the artwork. These experts typically examine the condition of the surface paint to deliver a verdict.
They can’t, however, push or pull on the canvas beneath the paint—the artwork’s structural support—to test for stability. That type of rough handling would be “unthinkable” for a masterpiece, says Marta Oriola, a lecturer and art conservator at the University of Barcelona. “So you often cross your fingers” during shipping, she adds.
To provide conservators with a quantitative tool for diagnosing the “health” of a masterwork’s canvas, Oriola teamed with chemist and heritage scientist Matija Strlič of University College London and colleagues. The researchers developed a technique based on near-infrared spectroscopy to nondestructively analyze a canvas from the back of the painting (Anal. Methods 2013, DOI: 10.1039/c3ay41094c).
Older paintings sit atop canvases made from a variety of natural, cellulose-based fibers: cotton, jute, or linen, to name a few. The challenge in preserving these materials is that “cellulose is not stable in acidic environments,” Strlič says. After years of exposure to environmental contaminants, canvas fibers become more acidic, which leads to cellulose breakdown and a general weakening of the overall artwork.
By experimenting with a group of nonvaluable canvases from the 19th and 20th centuries, Strlič, Oriola, and colleagues created a model for strength analysis that correlates a painting’s acidity and degree of cellulose breakdown with fiber-optic near-IR measurements. Then they carried out near-IR spectroscopy on the backs of 12 paintings by famed surrealist Salvador Dalí. These works were made available by Spain’s Gala-Salvador Dalí Foundation.
Although the researchers determined that all these masterworks were stable enough for travel, some of them have stained or discolored splotches that need to be monitored, Oriola explains.
Museum conservators usually have the expertise to make art-stability assessments qualitatively, without fancy instrumentation, says Francesca Casadio, director of conservation science at the Art Institute of Chicago. “But there is great value in developing these fairly quick, noninvasive, and objective means of rapidly assessing large collections.”