The Chemistry of Art

City College chemistry professor John Lombardi, right, and Metropolitan Museum chemist Marco Leona discuss joint projects at the Met.

One day a few years ago, City College chemistry professor John Lombardi got a phone call from a peer with an unusual specialty. Marco Leona was calling from the Department of Scientific Research at the Metropolitan Museum of Art - a subterranean lab that even the most avid patrons of the museum might be surprised to know exists.

The museum scientists' primary mission has been to develop better ways of preserving works of art - everything from determining the optimal interior climate for a Botticelli to discovering that a display case made of plywood produces organic vapors that can corrode a silver vessel from the time and place of Alexander the Great. But Leona, a chemist who heads a staff of eight, has a personal interest that veers down a different avenue of art history. He's made a specialty of identifying the materials - down to the molecular level - used by the artists whose works fill the Met and the world's other preeminent museums. It's less about conservation than about history and authenticity. "The brushwork of a painting could look like a Rembrandt, but we're interested in seeing if the trace elements match," says Leona. "So there's an element of forensic science."

The problem for Leona was that even the best available techniques made it nearly impossible to identify the molecular compounds in centuries-old pigments and dyes without damaging the artwork. "You can't return a painting to the collection full of holes," he notes.

Print of 1895 Japanese Kabuki theater ad being studied for

That's where John Lombardi came in. The City College chemist is a leading light in the field of Raman spectroscopy, a technique that uses laser beams to scatter and then identify the molecules of a substance. Leona thought the technology could put his work on a fast track, perhaps leading to dramatic developments in his field. In 2005 he met with Lombardi and the two decided to collaborate. They sought a grant from the National Science Foundation but were turned down because the work was judged less basic science than practical application. They found another source of funding in an unlikely place. "It was a solicitation from the Department of Justice," Lombardi says. "They were interested in forensic applications for identifying trace materials. We said, 'You know, that's what we do, after all.' "

With a three-year, $300,000 grant (renewable this year), the chemists have gone on to accomplish what they hoped, and then some. They've used Raman spectography to positively identify so many different substances in so many disparate works of art that they've produced more than two dozen scientific papers.

The key from the beginning, Lombardi and Leona agree, was not just the technology or their own expertise. "We both saw that a way to make this go forward was to include City College students," Leona says. "They could work on the problem, go back and work with John on more in-depth approaches so we could really make progress."

That they did. Lombardi's students - two post-doctoral chemists, two graduate students and four undergraduates - have helped Leona and Lombardi identify and catalogue some 50 compounds in dyes from all over the world and many centuries. "It's painstaking work," says Lombardi. "One molecule at a time." He and Leona have established a database that they and their colleagues at other museums can use to find matches in works that are being examined for practical reasons - authentication - or historical analysis.

"A whole group of materials is now within reach," says Leona. "Before, we could say, 'I think this was painted with this material, but I can't tell you because I can't remove enough of it to study with available techniques and without destroying it. Now we can take an essentially invisible piece of a work of art and say it was dyed with carminic acid, which comes from cochineal bugs, which are used in lipsticks and pink sodas."

Leona at one point used the Raman spectrometer to examine an object the museum was considering for acquisition: a rug of historical significance, said to have been the work of a renowned 16th century Romanian weaver. The laser generated an analysis that showed that the dye in the rug wasn't available until three centuries later - right around the time a famous forger of these rugs was known to be active. It was the first time one of the suspected forgeries had been scientifically proven. "It's like the difference between a police lineup and DNA," says Leona.

The Leona-Lombardi team's work has caught the attention of museum and research chemists alike, many of whom came to hear Leona discuss it at a recent meeting at the National Science Foundation. Though the research was considered outside the NSF's formal criteria for funding when Lombardi and Leona began, the results have apparently expanded the foundation's horizons. "My conversations with them continued," says Leona, "to the point that they got interested in the general topic of fundamental scientific research on cultural heritage."