Atomic oxygen removes soot from paintings

Two rocket scientists may have solved a particularly vexing problem facing art conservators. Many paintings damaged by smoke sit in storage, undisplayed and unappreciated, because no one has found a good way to clean them. Now, scientists from NASA are finding that atomic oxygen, which exists in Earth's upper atmosphere and chews away materials on orbiting satellites, may give conservators the tool they need to tackle this problem.

 Dabbing organic solvents onto a painting can clean off some kinds of soil, but it often does more harm than good. A shower of atomic oxygen, on the other hand, can remove layers of soot without anyone's ever having to touch the surface. Sharon K. Rutledge of NASA's Lewis Research Center in Cleveland reported the finding at the Materials Research Society meeting in Boston last week.

 After being approached by the Cleveland Museum of Art, Rutledge and her colleague Bruce A. Banks enlisted the help of the Cleveland Fire Department to expose samples of cotton canvas coated with acrylic gesso to smoke from a fire. Acrylic gesso is used to prepare surfaces for paint.

 The samples hung on a wall inside the fire department's training facility while several pieces of furniture burned. A section of an oil painting was exposed to a motor oil fire, which covered it with a layer of black soot.

 The researchers placed the samples in a vacuum chamber and bombarded them with atomic oxygen. They measured how well the samples reflected light before and after the cleaning. Black carbon from the oil fire came off in only 1 hour, whereas soot from the house fire took up to 23 hours, Rutledge says.

 House fire residue is a mix of many materials and is therefore very difficult to remove, says Marion F. Mecklenburg of the Smithsonian Institution's Conservation Analytical Laboratory in Suitland, Md. Fumes from melting synthetic materials like polyester, nylon, and rayon deposit "a coat of hot plastic onto the surface," he says. Atomic oxygen reacts with the carbon-based materials, turning them into carbon dioxide, carbon monoxide, and water.

 A hand-held atomic oxygen device that doesn't need a vacuum would make the technique practical for art conservation, says Rutledge. For now, though, the NASA researchers are trying to scale up their experiment by building a large vacuum chamber that can hold a painting measuring 5 feet by 7 feet.

 Although atomic oxygen alters the paint slightly and the vacuum may dry it out, Mecklenburg says he thinks "it's worth exploring." Conservators may have to "accept a modicum of damage. It's the lesser of two evils."