The da Vinci method: Shadow strokes

Economist
July 22, 2010

The Mona Lisa’s lure is so strong that Louvre Museum officials find it wise to keep her safely stowed behind bulletproof glass. She is let out of her protective cage once a year, for a whiff of fresh air. And this is when many a researcher would love to get their hands on Leonardo da Vinci’s most famous muse, in order to find out more about how she was painted.

For a long time, scientists and curators have wondered how da Vinci created shadows on her face with seemingly no brushstrokes or contours. Art experts call this shadowing technique sfumato—like the Italian word for smoke, fumo. Experts have long suspected sfumato shadowing has something to do with the glazes that da Vinci used above the paint layer. But proving this has been difficult because snatching a sample of the Mona Lisa’s face for chemical analysis is, unsurprisingly, frowned upon.

Instead, Louvre scientists led by Philippe Walter tried to solve the mystery using a hands-off technique called X-ray fluorescence, which can divulge details about the thickness and chemical composition of a painter’s individual brush strokes without damaging artwork. Focusing X-rays on faces in seven of da Vinci’s masterpieces, including the Mona Lisa, Dr Walter’s team found that the artist would first paint in the basic flesh tones. Then da Vinci applied up to 30 incredibly thin strokes of glaze above the flesh tone—many just a few micrometres thick.

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