March 7, 2001: Features

Saving old stones
Engineering professor George Scherer takes a scientific approach to art and architecture

By David Marcus

George Scherer in an Alexander Hall stairwell, where sodium sulfate crystals that apparently seep in from outside are damaging the walls.

Late on a raw, gray afternoon in November, Princeton professor George Scherer and a pack of his students are standing outside the Cloisters, the northern Manhattan branch of the Metropolitan Museum of Art that specializes in medieval art and sculpture. Bracing against the sharp wind off the Hudson, the group squints up at the weathered gargoyles on the side of a 12th-century stone chapel.

The scene would be unremarkable - after all, the art history class trip is a Princeton tradition - except the 50-year-old Scherer teaches civil engineering, not art history, and his students are studying the decay, not the creation, of art and architecture made of stone and mortar. The trip is part of Civil and Environmental Engineering/Art History 105: Lab in Conservation of Art, a class combining art and science that Scherer offered for the first time last fall. He's trying to introduce nonscientists to materials science, which Scherer defines as "the study of the ways in which the structure of a material controls its properties, and the processing of the material controls its structure."

None of the 35 students in the class is an engineer. About a quarter of them are majoring in art history or plan to, and they value the course for their own reasons. "CEE 105 encourages us to think of art in material, scientific terms," says Kristin Roper '03. "In most art history courses, the discussion is limited to aesthetic qualities, while in CEE 105 we think almost exclusively in terms of preservation."

Preservation, and the class, begins at home. On a September tour of Princeton's campus, Scherer demonstrated the ubiquity of the destructive processes his students would study. He pointed out the erosion of the Woodrow Wilson School plaza's fleuri limestone by the repeated freezing and thawing of water; the corrosion of Clio Hall's Vermont Danby marble by acid rain; and the deterioration of Alexander Hall, which is falling apart in ways so varied an enterprising senior could write a thesis about the decay.

Scherer's interest in stone conservation evolved in a roundabout way. He earned his B.S. in 1972 and Ph.D. in 1974 from the Massachusetts Institute of Technology, then worked as a scientist at Corning Inc. and E. I. DuPont De Nemours & Co. At DuPont, Scherer became expert in sol-gel technology, a technique for making ceramics at low temperatures that is used to produce, among other things, the scratch-resistant coating on eyeglass lenses. In the late 1980s, he met George Wheeler, a research chemist at the Metropolitan Museum, at a conference where Wheeler discussed the use of sol-gel materials in preserving stone. "That was a revelation to me," Scherer says. "I had no idea that the technology had application to art."

Several years later, Scherer decided to switch careers. "It had always been my intention to go into academia, but I was having so much fun in industrial research that I had no incentive to leave," Scherer says. But as labs in industry began to cut back on basic research, he says, "I decided to do something different; namely, commit myself primarily to teaching."

Scherer and Wheeler kept in touch over the years, and the friendship came in handy when Scherer began teaching at Princeton in 1996. Charged with starting a research effort on the science of building materials, Scherer told Wheeler that he wanted to do work in art conservation, which, like materials science, involves the study of stone's decay.

The new professor had a lot to learn. "I started with no knowledge of the problems relevant to art," Scherer says. "For example, which kinds of stone are used in monuments and what kind of damage is observed to occur? George Wheeler has been educating me about those things, and about the repair strategies that have been tested."

Wheeler says that Scherer thinks about conservation differently than he does: "Professor Scherer works at a more fundamental level than I do. I'm sticking my fingers in the dike, and he is trying to design a better material to build dikes with by first understanding why and how they fall apart."

The two men consult frequently, and Wheeler has enlisted Scherer in the effort to conserve the chapel from the church of San Mart'n at Fuentidueña, a 12th-century structure whose apse forms part of the Cloisters. Like much of the museum, the chapel was disassembled in Europe and put back together on the northern tip of Manhattan in the 1930s under the aegis of John D. Rockefeller, Jr., who funded the Cloisters' construction.

It's the Fuentidueña apse that Scherer's shivering students are staring at on their November field trip as Wheeler explains the conservation challenges the building poses. "There's every mode of deterioration of stone you could have," Wheeler says. The chapel's dolomitic limestone is acid-soluble and hence susceptible to acid rain. The stone is particularly vulnerable to damage from freezing, not a problem in Segovia, Spain, where the rest of the chapel still resides, but a considerable one in Manhattan. Five to 10 percent of the stone seems to be composed of clay minerals that expand when wet, hastening the stone's decay. One of Scherer's graduate students, Inma Jimenez Gonzalez, is writing her dissertation on the durability of the potential chemical treatments for the chapel's deterioration.

Gonzalez also helped Scherer design the labs for the class. "We really focus on illustrating experimentally principles that are too often only described," she says. For example, in one lab, the students observed the effects of dripping nitric acid - the destructive agent in acid rain - on various kinds of stone. Even in a three-hour lab, the acid's corrosive effects on limestone - various kinds of which comprise both the Wilson School plaza and the Fuentidueña chapel - are substantial.

In designing the labs Gonzalez and Scherer had to compress into a few weeks' time processes that attack buildings over years. But on occasion, the requirements of the academic calendar and the rate of decay of an artifact coincide, as they have in the case of the Princeton Art Museum's Egyptian sculptures.

In 1950 the Art Museum received more than 200 stone relief sculptures from the Metropolitan Museum, which had procured them in an expedition to Egypt in the 1920s to excavate the tomb of the Vizier Nespekashuty (c. 600 BC), according to Art Museum curator Michael Padgett. The reliefs, which are adorned with scenes depicting offering-bearers and other elements of a funerary cult, were valued so highly by Princeton that it stuck them in the Armory, near the football stadium, for a half-century. In the summer of 1999, the museum's curators became concerned enough about the reliefs' condition to transport them to a secure, climate-controlled room at the museum.

Ironically, the reliefs preferred benign neglect to conscientious conservation; they have begun to decay since arriving at the museum. Padgett says they suffer from an "inherent vice, an internal condition in an art object that, more or less independent of external conditions, leads to its inevitable deterioration." To help solve the mystery, the Art Museum called in Scherer.

The professor discusses the reliefs frequently with Wheeler, but chemical and structural analyses the two have supervised have yet to reveal the cause of the decay. Three of Scherer's students are helping to photograph the reliefs and enter descriptive information about them into a database. Having studied the science of how materials decay, the volunteers are experiencing a more visceral aspect of art conservation. Says Alexandra Greist '03, "I've learned how frustrating it is when a piece of art that has survived for thousands of years in a relatively exposed state suddenly starts to crumble into dust as soon as interest is taken in its conservation."

That frustration hasn't impeded her fascination with the subject. Greist wrote a paper for Scherer's course in which she proposed that the effects of the move on clay in the stones might be responsible for the decay. "When changes in humidity are gradual, the stone shrinks or expands slowly and consistently," Greist says, explaining her theory why the reliefs suffered little damage at the Armory. "When the change is sudden the outer layers of stone dry much more quickly than the inside, putting great stress on the outer layers. The 'skin' of the stone shrinks and cracks because the inside is still swollen with water. The outer crust is like the peel of an orange that has rotted; the brittle peel cracks and breaks around the water-logged fruit."

Scherer liked Greist's work enough to suggest that she consider majoring in civil engineering, but he couldn't persuade her to set aside art for science. Still, he values his students' newfound grasp of materials science at least as much as they enjoy the art through which he has taught his subject, he says. "It has been gratifying to see how much the students appreciated hearing about the technical side of the conservation issue."


David Marcus '92 is a reporter at the Daily Deal in New York City.