The person in the cherry picker is giving an odd sort of truth to Walter Pater’s definition of art: “All art does but consist in the removal of surplusage. ” For Phoebe Dent Weil is removing surplusage from the statue of Saint Louis that resides in Forest Park, St. Louis, just as she would like to see done to all the statues and monuments that stand in the parks, plazas, squares, and civic centers of nearly every city in the nation.

The ambition began more than a decade ago, when it was discovered that outdoor statuary in Venice, some of which has endured for hundreds and even thousands of years without significant change, was suddenly showing signs of swift and irreversible deterioration. The culprit was identified as air pollution so thick and insidious that it had caused more damage in the past fifty or sixty years than in the two thousand years that preceded it. Nor was the situation likely to improve, for experts predicted that levels of pollution would nearly double over the next century; neither was the problem confined to Venice; air pollution had become a commonplace in urban regions all over the world.

Bronze statuary was most profoundly affected, it was determined. Not only did pollution give it a runny green patina and cake it over with a sooty crust as hard as glass, but chemical fallout…particularly sulfur dioxide—attacked the metal directly, wasting it away, riddling it with pits, and causing the exudation of core material. Since most bronze statuary was cast no more than a quarter of an inch thick, it was not difficult to imagine ätime when much of it would be reduced to filigree.

Art conservationists around the world began investigating the problem. At Washington University in St. Louis, Mrs. Weil, who has degrees in art history and art conservation and has studied at such diverse institutions as the Institut Royale du Patrimoine Artistique in Brussels and the Nelson Gallery in Kansas City, got together with her husband, Mark, a professor of art and archaeology, Peter Caspar, a professor of chemistry, Robert Walker, a professor of physics, and other specialists, and by 1974 the team had a solution.

The process they developed is called “glass-bead peening.” It is adapted from a system for cleaning the inside of jet engines in which minuscule glass balls are driven against a surface under air pressure. What is particularly remarkable about the technique when applied to bronze statuary is that it not only blasts away the incrustations of decades, but the glass beads themselves shatter into microscopic bits and imbed themselves in the surface of the metal, giving the statues an invisible coat of protection. After the peening, statues can then be patinated to a golden brown with copper and iron nitrates applied with an acetylene torch, then given a final preservative coat of acrylic resin.

Under the auspices of Washington University’s Center for Archaeometry,