Mona Lisa's smile

French researchers studied seven of Paris's Louvre Museum's Leonardo da Vinci paintings, including the Mona Lisa to analyse his technique that gave his works their dreamy quality.
Specialists from the Center for Research and Restoration of the Museums of France found that da Vinci painted up to 30 layers of paint on his works to meet his standards of subtlety. Added up, all the layers are less than 40 micrometers, or about half the thickness of a human hair, researcher Philippe Walter said.
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