Among the diverse items she has scrutinized in recent years are Civil War-era weapons, copper weather vanes, and works by Picasso, Matisse, and N.C. Wyeth.
About 20 U.S. museums, including the Philadelphia Museum of Art, now have labs like the one at Winterthur, equipped with sophisticated instruments to identify artistic materials and techniques of centuries past. The Art Museum, whose scientists recently helped in refurbishing the newly reopened Rodin Museum, is hosting an international conference next month on a laser-based art-sleuthing method.
Such labs are run by cautious folks, quick to point out that science can at best provide partial answers.
The goal, generally, is not to tell who painted a painting - not that there is even a machine that can do that. More commonly, the aim is to reveal how an object was created, both for art history's sake and to determine the best way to conserve the artwork for future generations.
Mass, for example, analyzed deterioration in Joy of Life, an iconic Matisse owned by the Barnes Foundation, so that the museum could decide how best to display it at its new location on the Benjamin Franklin Parkway.
The answer? Low light, because some of Matisse's paints were unstable and prone to oxidation.
"It looks like Matisse was using several different tubes of cadmium yellow," said Mass, 44, of Berwyn.
Not 'Antiques Roadshow'
Most of the chemist's work is on objects in Winterthur's collection, whose authenticity is not in doubt. But among the outside objects that she and her colleagues analyze, many are of uncertain origin.
No scientific test can prove that an object is the real thing. But plenty of times, Mass can say when it is not - if, say, a modern material was used to make something that purports to be from the 18th century.
"We often say we're kind of the opposite of the Antiques Roadshow," Mass said, referring to the TV show in which owners often learn they have treasures in the attic.
Currently in her lab are two examples of Fraktur - Pennsylvania Dutch-style illuminated manuscripts - said to be the work of 19th-century artist Samuel Bentz.
Fakes, says Mass. Tests show the inks are of modern vintage.
Mass has a cheerful demeanor and takes an obvious joy in the gifts of artists whose work she studies. So it pains her when she must tell an owner that an object is not legit.
"It's so sensitive and so awful to explain," she said.
A happier end seems likely for the would-be van Gogh.
The 7-by-83/4-inch canvas depicts rows of tilled earth, a wheeled cart, and an industrial building. It was purchased from a small gallery by a specialist in 19th-century paintings, who asked not to be identified. Mass has found that the artist's palette included yellow ocher, Prussian blue, and bone black, a paint made from burned animal bone - all available in van Gogh's time.
Kristin deGhetaldi, a University of Delaware doctoral student who is helping to study the painting, is now doing further research on whether van Gogh used those materials.
At most, they will be able to say whether the work is "consistent with" van Gogh - which seems to be the case. The final word will rest with experts at the Van Gogh Museum in Amsterdam.
If it's the real thing, it likely would be worth millions, deGhetaldi said. If not, she said: "Drop a few zeroes."
It began with art lessons.
When Mass was just 6 years old, an art teacher came to her family's house in Livingston, N.J., once or twice a week. The teacher would put up a picture of a painting by, say, the Spanish artist Joan Miró, and ask Mass and her two sisters to copy it.
"It made a huge impression on me," Mass recalled.
She also showed an early aptitude for science, and went on to major in chemistry at Franklin and Marshall College. She also studied Greek and Roman art and archaeology, drawn to their classic beauty.
But then, as now, there were no formal academic programs in the United States for scientists who wanted to apply their analytical skills to works of art. So Mass plotted her own course.
At Cornell University, where Mass got a master's degree and a doctorate in inorganic chemistry, one professor had a daughter-in-law in the art-conservation field. He urged Mass to explore both of her passions.
While classmates were taking jobs at places such as Bell Labs and Corning Glass, Mass landed a fellowship at the Metropolitan Museum of Art in New York City. The museum did not have a science department then, but Mass made the most of it, applying her knowledge to Roman glass and other antiquities.
"You are really fortunate if you have one thing you are passionate about and you're able to focus on that area," she said. "To have two things. . . ."
She came to Winterthur in 2001, when her husband, a physicist, took a job with Merck. Mass also teaches at the University of Delaware.
Scientists have been analyzing art at least since the early 1800s, when the renowned chemist Humphry Davy studied ancient paint samples from the ruins of Pompeii.
But it is only in the last decade that the field has really taken off in the United States, thanks in large part to the Andrew W. Mellon Foundation.
Since 2000, the New York-based philanthropy has made more than $50 million in conservation-science grants to museums and universities. Much of it went to endow positions, including one at the Art Museum.
Another boost has come from an analytical technique called Raman spectroscopy, the focus of the Art Museum's conference next month. The method is not new, but was not especially useful to the art world until refinements were made in the last decade, said Beth Price, head of the museum's lab.
Raman spectrometers use laser beams to identify the chemical composition of a sample by recording the characteristic pattern in which the laser light is scattered.
Another common technique relies on infrared beams to accomplish the same end; Raman is good for identifying certain substances, while infrared is better for others.
One recent afternoon, Mass used an infrared spectrometer to analyze samples from The Blue Room, a 1901 Picasso owned by the Phillips Collection in Washington.
Mass had removed the merest of paint flecks from 14 locations on the Picasso, and brought them back to Delaware in small plastic bags.
She placed a sample on the infrared device, then waited as the results were graphed on a computer screen. Because the line on the graph rose and dipped at certain telltale points, she could tell the paint contained a barium compound, likely used as a filler in the paint, and cobalt, which was used to accelerate drying.
"You can spend an entire afternoon on a microscopic sample like this," Mass said.
Mass earns rave reviews from the two worlds that she straddles, art and science.
Elizabeth Steele, head of conservation at the Phillips museum, said the work Mass does is invaluable. "We would never have this sort of thing in-house," Steele said.
Likewise, Mass' fellow scientists appreciate that she is making their techniques known to a broader audience.
For example, the Winterthur chemist has analyzed several paintings using a synchrotron, a high-intensity X-ray source, at Cornell University. It is primarily used in more traditional fields of science, such as structural biology and materials engineering.
But Mass' ardor for studying artwork is infectious, said Arthur Woll, a senior research associate at Cornell.
"She's really a conduit to this whole world for us," Woll said. "Without her, first, we wouldn't know what problems exist. We also wouldn't know any of the people involved, or what questions to ask."
Contact Tom Avril at 215-854-2430 or firstname.lastname@example.org