RALEIGH - You never know when inspiration will strike: painters and sculptors will tell you that. So will musicians and songwriters. It’s true even for scientists.
Duke University chemistry professor Dr. Warren S. Warren was in London attending a conference when he decided to visit the National Gallery.
“And I saw an exhibit on the technology that was being used for art imaging, for detecting forgeries, and I realized that the technology was 30-40 year-old technology in terms of modern imaging,” says Warren.
Warren was working with chemists, biologists, and doctors at Duke University Medical Center on a pump-probe laser that captured images of melanomas, or skin cancers, so they could be analyzed.
“To be able to look at a mole and see if it’s a melanoma or something you don’t have to worry about is a wonderful diagnostic tool,” adds Warren. “But then I thought that the same issues that come to bear in trying to image skin deep below the surface are the same issues that arise when trying to look at a painting below the surface.”
So Warren began investigating whether his device could uncover the secrets underneath layers of paint without damaging the art, just like it did under layers of skin without hurting the patient.
Warren contacted William Brown, the Chief Conservator at the North Carolina Museum of Art and proposed a collaboration between Duke University and the museum to find out whether a nondestructive, deep imaging laser that is used in melanoma research could be used in art conservation.
The laser sits atop a table that “floats” on legs that are filled with nitrogen and takes up about the size of a standard room. There are two lasers that resemble giant black boxes on one corner. There are beams of two colors that are directed through 20 lenses and six prisms, guided, narrowed and aimed to focus on a target.
After months of study, they decided to test their idea on The Crucifixion, a 14th Century painting by Italian artist Puccio Capanna that is on display at the museum.
“It’s beautiful, it’s jewel like, it’s reminiscent of manuscript painting because it’s got everything you would want in a precious little painting with the gold leaf, and there’s punch work in the halos,” says Brown, as he removed the wood,which the artist used as his canvas, from its protective frame. “The blue is fantastic and that’s why we are here because of the blue. Usually to have a blue as thick as this in a painting is unusual.”
The painting depicts the Crucifixion of Christ, with Mary, his mother, weeping in sorrow next to the cross. There are others gathered around the cross as well, with an angel near Jesus’ head. The entire background is gold leaf, with gold highlights and gold halos on the figures. But it’s the deep blue of the Virgin Mary’s robes that conservators are focused on. It’s believed to be lapis luzuli, a rare mineral found only in Afghanistan.
Until now, a conservator would use a scalpel to remove a tiny chip from the painting and study it under a microscope. That’s not a good thing to do with a painting dating back to 1330.
The pump probe laser will allow conservators to scan through the layers of that dark blue paint without hurting the art.
That’s because the device uses two low-energy laser pulses of different colors in a laser-scanning microscope. The beams are focused on the area to be examined. The pulses are timed. The first beam pumps the pigment while the second probes what happened to the energy left by the first one. Each pigment has a unique energy signature. Images are taken with different colors to study the wide range of pigments. Researchers can zoom in and out, much like someone probing a layer cake with a fork, to separate the colors and see what was originally on the canvas.
The painting it locked into a cradle on the laser and the beam is focused on a specific area and fired. The total power on the painting is harmless because it is less than what a laser pointer emits. Tana Villafana, a graduate student who worked on the project, is fascinated by the story about the painting that is uncovered during the analysis.
“This piece was probably in someone’s personal sanctuary at home and now we are putting lasers on it, so it’s exciting and scary at the same time,” says Villafana.
The image slices are 100 microns by 100 microns. Turning a roller ball moved the laser deeper into the layers of paint. A computer screen shows the images. The first thing Martin Fischer, an associate research professor discovers, is that the paint is pure lapis lazuli.
“So we start at the surface and we gradually go through the layers, and you can see the crystals come into focus. And then they go away because we are going through another layer until we get all the way to the end,” says Fischer, as he rolls the tracking ball. “We have mixed lapis lazuli with a Cimarron Red, so this blue is the actual lapis crystals. Lapis is a ground up rock and these are the actual crystals.”
“You can see here this is a pure layer of lapis lazuli, with the drapery folds in a layer of black paint,” Brown adds as he glances between the computer screen and the priceless work of art nestled in a cradle at the end of the laser. “It’s not done realistically, it’s all very symbolic and schematic.”
The artist’s use of pure lapis suggests the patron of the work was very wealthy. The mineral would have to be imported into Italy from Afghanistan and then brought to Florence where the work was painted. The discovery also adds to the importance of studying what’s believed to be a companion work that is now in the Vatican museum. Matching the paints would confirm the works were painted together and most likely used in a church before they were separated. Brown says the museum is working on that idea.
For now, Dr. Warren is happy his idea, first conceived in a London museum, worked as well as he thought. He’s now working on a portable laser that could be taken to museums rather than having the artworks brought to Duke.
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