Scientists have unlocked another Mona Lisa mystery by determining how Leonardo Da Vinci painted her near faultless skin tones. Using X-ray techniques, a team “unpeeled” the layers of the famous painting to see how the Italian master achieved his barely perceptible graduation of tones from light to dark. The technique used by Da Vinci and some other Renaissance painters to achieve this subtlety is called “sfumato,” and unraveling it allowed the scientists to determined the composition and the thickness of the paint layers. Philippe Walter, a senior scientist at the Paris-based Laboratoire du Centre de Recherche et de Restauration des Musees de France, told CNN: “This will help us to understand how Da Vinci made his materials… the amount of oil that was mixed with pigments, the nature of the organic materials, it will help art historians.” Walter and his colleagues used X-ray fluorescence (XRF) spectrometry to determine the composition and thickness of each painted layer of the Mona Lisa in the Louvre Museum in Paris, where the painting is normally kept behind bulletproof glass. Art historians believe it was painted by Da Vinci in 1503. They found that some layers were as thin as one or two micrometers and that these layers increased in thickness to 30 to 40 micrometers in darker parts of the painting. A micrometer is one thousandth of one millimeter. They believe this characterizes a technique of painting that uses a glaze, or very thin layer, to build up shadows in the face. – from CNN