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. Glaze is mostly translucent, but da Vinci would also slip in small amounts of pigments, such as manganese and lead oxides. By applying many thin coats of this adapted glaze, he achieved the smoky shadowing he became famous for.
The da Vinci method: Shadow strokes, The Economist, July 22, 2010
