When hunting for historical information or preserving a piece of art, conservationists traditionally turn to scalpels to remove paint samples. This comes at an obvious cost to the painting though, not to mention that only sparse samples from background, borders, or already cracked regions may be removed for microscopic analysis using this approach.
But now, Duke University chemists collaborating with art conservators at the National Museum of Art and North Carolina Museum of Art have come up with an ingenious solution to this dilemma -- adapting a new 3-D laser imaging microscopy technique involving a femtosecond pump-probe laser system developed to detect cancer in skin to uncover the complex structural details of centuries-old artwork, without having to touch the canvas.
Warren S. Warren, Director at the Center for Molecular and Biomolecular Imaging at Duke, who led the research team, got the idea to transfer his lab’s microscopes to the art world after visiting an exhibit on art forgeries at The National Gallery in London.
“By the time I finished, I realized that the technologies that people were using to analyze artwork were 30 to 40 year-old bio-imaging technologies,” said Warren. “I started asking what we might learn if we started adapting state-of-the art ideas that are being used in biomedical imaging labs to this specific problem.”
To find out, Warren’s lab analyzed over a dozen Renaissance works at two museums, beginning with Puccio Capanna’s The Crucifixion (circa 1330), using his 3-D laser imaging technology.
Placing the painting in the apparatus, a sequence of ultrafast pulses were used to electronically excite molecules within the paint, which they probed as they relaxed to their normal states.
By charting molecule resettling rates in different paints, the team was able to reconstruct 3-D cross-sections of the canvas. Then using near-infrared imaging, individual pigments within each virtual layer could be isolated.
To demonstrate the potential of the approach, the team successfully image-mapped the Virgin Mary’s robe, which was found to contain unusually heavy layers of the deep blue pigment made from lapis lazuli—a highly coveted resource that was much more expensive than gold at the time the painting was commissioned.
Warren said the method could one day reveal key information from a variety of famous historical artworks—from understanding how the 8000 Terracotta Army sculptures found in the Shaanxi province of China were constructed in 210–209 BC, to reimagining the original multicolor surfaces of ancient Greek statues before they became completely whitened in the 17th and 18th centuries.
At the moment however, Warren says that large-scale research of this type will require a more transportable version of the laser system.
“In principle, this is something we know how to do,” explained Warren. “All of the miniaturization technology that we need is being done for the biomedical research community anyway, so we will piggyback on that technology development.”