March 7, 2001:
Engineering professor George Scherer takes a scientific approach
to art and architecture
By David Marcus
Scherer in an Alexander Hall stairwell, where sodium sulfate
crystals that apparently seep in from outside are damaging
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
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
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
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
David Marcus '92 is a
reporter at the Daily Deal in New York City.