Mona Lisa's x-ray uncovers da Vinci's painting secrets
16 July 2010 Last updated at 22:23 BST
French scientists are confident they have uncovered a few secrets of the Mona Lisa.
The researchers x-rayed seven of the Louvre Museum's Leonardo da Vinci paintings, including the Mona Lisa, to analyse the master's use of successive ultra-thin layers of paint and glaze.
They found that da Vinci painted up to 30 layers of paint on his works to meet his standards of perfection.
The technique called "sfumato", allowed da Vinci to give outlines and contours a hazy quality and create an illusion of depth and shadow.
Mona Lisa image courtesy: V.A. Sole/ESRF