Researchers have decided to get personal with Mona Lisa–by irradiating her face. In a study recently published in Angewandte Chemie, researchers trucked around the Louvre to look at nine faces painted by Leonardo Da Vinci with a portable X-ray machine.

Their particular technique, as reported by the BBC, is called X-ray fluorescence (XRF) and is a way to uncover the layers of paint without damaging the paintings. By looking at this layering, they learned more about Da Vinci’s brush strokes and a technique called sfumato, which he used to hide transitions between dark and light areas and to create realistic shading.

The Da Vinci researchers aren’t the only X-ray art historians. Another recently published study looked at “Mayan blue”–a long lasting pigment made by the civilization that lived in Central American from 2500 BC to the 1600s.

Archeologists were impressed with Mayan blue’s resistance to fading, given that most of the other colors used in Mayan artworks lost their vividness long ago. As reported by Technology Review, Catherine Dejoie at the Néel Institute in Grenoble used X-ray diffraction and also examined the blue samples’ weight changes during heating (called thermogravimetric analysis) to uncover the pigment’s secret.

The researchers knew that the Mayans made their blue by heating the pigment with palygorskite (a type of clay); their analysis showed that this heating allowed the pigment to enter tiny channels in the clay which are sealed after the mixture cools, protecting and keeping the pigment true blue for centuries.

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Image: Wikimedia