Pump-Probe Laser Imaging to Improve the Arts

A pump-probe laser technique designed to diagnose melanoma has now been applied to art, uncovering paint pigments and layering techniques noninvasively to provide historical insight into works of art.

The interplay of art and science is subtle but important, and now North Carolina Museum of Art (NCMA) conservators and Duke University scientists are collaborating to better recognize the paint and other materials used in the creation of the 14th-century “Crucifixion” by Puccio Capanna using a nondestructive pump-probe laser and an Er:YAG laser cleaning tool. The knowledge gained from the collaboration, such as how to identify different colors in complex mixtures, could prove useful in identifying different biological tissues, said Dr. Martin Fischer, an assistant research professor at Duke.

“This collaboration with Duke dovetails perfectly with the museum’s initiative to share resources with local universities, bolstered by a research endowment from the Andrew Mellon Foundation in support of art scholarship and conservation science,” said William Brown, NCMA chief conservator. “The NCMA’s Art Conservation Center has had the privilege of working with this group of distinguished scientists from Duke, and we look forward to what the next year will bring.”

The pump-probe laser being used at Duke on “Crucifixion” by Puccio Capanna. Courtesy of William Brown.

Pump-probe laser imaging is a technique originally designed by Dr. Warren S. Warren, director of Duke’s Center for Molecular and Biomolecular Imaging, to use in the diagnosis of melanoma. Now applying the technique to art, conservators can better distinguish the materials used in artwork. Paint pigments carry an identifiable molecular signature, meaning materials used by an artist can be identified through scientific analysis.

“Dr. Warren assumed that, just as with skin lesions, yellowed varnish and paint layers could be imaged by his laser to distinguish original paint from restoration, helping us understand the intended beauty of centuries-old paintings,” Brown said.

As part of the collaboration, the investigators trained with Dr. Adele de Cruz, adjunct associate professor at Duke, who created the Er:YAG laser technique, or laser scalpel, for art conservation nearly 15 years ago. The laser enables conservators to remove old, degraded varnish coatings from paintings and other works of art with a high amount of control and precision.

“Paintings once considered impossible to clean by conventional methods can now be returned to their former glory,” Brown said.

Brown has volunteered Capanna’s “Crucifixion” as the first full piece of art for the scientists to analyze, hoping that the laser system may eventually identify the paint pigments and layering techniques Capanna used. It may also help confirm whether the painting was originally part of an altarpiece at the Vatican.

The technique could improve conservation and restoration by informing treatment choices to ensure that only old, degraded coatings are removed — not original paint. Additionally, the technology allows conservators to noninvasively analyze works of art. Other methods of paint analysis require cross-sectioning or the removal of small paint chips.

Dr. Adele de Cruz, adjunct associate professor at Duke University, and William Brown, chief conservator at the NCMA, using the Er:YAG (laser scalpel) in the Museum conservation lab. Images courtesy of NC Museum of Art; Karen Malinofski, photographer.

Pump-probe laser imaging avoids this by providing nondestructive, 3-D, chemically specific images of various historical pigments and paint layering. The total laser power on the painting is less than that of a common red laser pointer.

“Given that each work is irreplaceable, destroying even a very small part of the painting is a difficult choice for a conservator, who, like a doctor, is ethically obligated to do no harm,” Brown said.

The analysis method can also reveal the historical nature of a work of art by uncovering where pigments originated. This information may help confirm details of a work’s origin and help authenticate the art.

“What’s so satisfying for me is the interdisciplinary nature of this collaboration,” Brown said. “I’m able to work with scientists from different fields and clearly benefit from their expertise by learning new scientific methodologies and gaining a greater understanding of the material nature of the art.”

For more information, visit: www.duke.edu