The bag of dried cochineal insects and the half-million-dollar laser microscope in chemistry professor Kristin Wustholz’s laboratory represent the past and future of the science of art.
For thousands of years, lowly bugs like this have been ground up and processed to produce rich red paints, while the laser microscope is being used increasingly to study those old pigments at the molecular level, helping conservators understand exactly what went into great works of art. Literally.
The laser technology is called surface-enhanced Raman scattering spectroscopy, or SERS, developed in the 1970s but only in the past decade or so adapted to study the makeup of oil paints. Wustholz is a pioneer in this groundbreaking technique.
Now, this summer, one of her graduate students at the College of William and Mary in Williamsburg will be taking that SERS expertise to the Netherlands and applying it to masterpieces by the 17th-century Dutch artist Rembrandt.
“This is, for me, a once-in-a-lifetime opportunity,” said Shelle Butler, a 34-year-old Richmond native and U.S. Air Force veteran working on her master’s in chemistry. “Especially being able to almost just have a religious experience with being able to work with works by Rembrandt.”
She has been instructed by the owners of the artwork not to say which painting or paintings she’ll be analyzing. But she’ll be working at the Rijksmuseum in Amsterdam.
That museum has Rembrandts in its collection, and according to the museum’s website, in January 2016, also became one of the new homes of a pair of Rembrandt portraits purchased in a joint venture by the Netherlands and France for a total of roughly $175 million.
The rare life-size portraits of newlyweds Marten Soolmans and Oopjen Coppit were painted in 1634 and remained in private hands for nearly 400 years. They’re considered the least-exhibited of Rembrandt’s works. Last year, they were displayed at the Louvre Museum in Paris for several months and then at the Rijksmuseum before being removed to the museum’s conservation workshop for restoration.
Butler’s summer project is funded through the competitive International Research Experiences for Students program of the National Science Foundation, in cooperation with Northwestern University and the Netherlands.
She believes it was her experience with the SERS technology in Wustholz’s lab and applying it to paintings from the Colonial Williamsburg Foundation that ultimately clinched her role in the Rembrandt restoration work.
“Actually, I’m not aware that they have actually used the SERS method,” Butler said of the Dutch museum. “I know that was the big draw for getting me onto the project.”
The technique involves taking a nearly microscopic paint sample and combining it with a paste of silver nanoparticles that, under a laser microscope, act as tiny antennae to broadcast the colorant it contains. That signal is called Raman scattering and gives a color its distinctive chemical fingerprint.
That fingerprint has real value in the art world, said Shelley Svoboda, painting conservator at the Colonial Williamsburg Foundation. By understanding the source of a colorant, conservators can better protect and preserve precious artwork.
Svoboda and Wustholz have been collaborating for several years now to analyze the oil collection at Colonial Williamsburg.
“We were the first to do SERS identification of pigments in oil paintings,” Wustholz said. “You would think that would have been done (already), but it was not. We were very excited to get in on that.”
She and Svoboda were also the first to use SERS for carmine, which is the pigment that comes from the cochineal insects.
For thousands of years, artists have used animals, vegetables and minerals to produce the pigments for their work.
“All artists made their own paints or had their studios make them,” Svoboda said. “They stored them in pig bladders, or not at all. And that didn’t last very long, so there was a lot of paint-making.
“It’s very time-consuming, and each of the pigments has its own ideal pigment binder or ratio. And it’s a real kind of experience that you have to gain by doing.”
Cochineal insects, for instance, are used to make a red “lake,” or red insoluble pigment, that was highly prized and expensive, often used to enliven flesh tones. A similar-looking red could be produced by the madder plant, and it was cheaper and more plentiful.
Depending on their source, paints can respond differently to environmental conditions.
Mineral compounds, for instance, are quite stable, while organic compounds made from plants and insects fade over time, especially when exposed to sunlight. In oil paintings, faded colors are known as fugitive pigments. SERS is so sensitive it can accurately identify the original color source for fugitives from a tiny speck of paint.
Research indicates Rembrandt used organic color bodies in his work, Svoboda said, “but it’s not possible to identify them without either having large sample quantities or the SERS technologies.”
Butler will be working with a handful of other students from other universities at the museum. Her job will be to use her SERS expertise to analyze red lakes in Rembrandt’s work, enabling the conservator to better preserve it, perhaps by managing its exposure to light sources.
“She’ll be working with some of the world-renowned conservation scientists,” Wustholz said. “I’m a chemist, and I don’t bring that expertise. She’s going to be working with people that do science on art every day. That’s a rare opportunity.”
For Butler, it’s also a taste of an emerging career path.
“That’s definitely the goal right there, is to do this forever,” Butler said. “And to push the field even further.”
Dietrich can be reached by phone at 757-247-7892.
