Scientists reveal process behind Da Vinci's sfumato

A 16th-century painting technique employed by Leonardo Da Vinci has been investigated by scientists, without needing to remove samples from the artist's great works.

Using X-ray fluorescence, the scientists examined the layers of paint built up on seven of Da Vinci's works, including the Mona Lisa, which is painted on a poplar panel.

They discovered some of the secrets of sfumato, a combination of technological innovation and artistic skill from the early 16th century.

In the case of Da Vinci, some layers of paint used were no thicker than two microns, leading to a total thickness of oil less than 40 microns deep.

The use of very thin layers is part of the sfumato process, combined with the properties of the pigments applied.

It is just one of the techniques that the scientists say allowed Da Vinci to replicate faces with high levels of detail and optical effects including blended shadows, soft transitions and subtly blurred outlines.