Specialists from the Center for Research and Restoration of
the Museums of France found that da Vinci painted up to 30 layers of paint on
his works to meet his standards of subtlety. Added up, all the layers are less
than 40 micrometers, or about half the thickness of a human hair, researcher
Philippe Walter said Friday.
The technique, called "sfumato," allowed da Vinci
to give outlines and contours a hazy quality and create an illusion of depth
and shadow. His use of the technique is well-known, but scientific study on it
has been limited because tests often required samples from the paintings.
The French researchers used a noninvasive technique called
X-ray fluorescence spectroscopy to study the paint layers and their chemical
composition.
They brought their specially developed high-tech tool into
the museum when it was closed and studied the portraits' faces, which are
emblematic of sfumato. The project was developed in collaboration with the
European Synchrotron Radiation Facility in Grenoble.
The tool is so precise that "now we can find out the
mix of pigments used by the artist for each coat of paint," Walter told
The Associated Press. "And that's very, very important for understanding
the technique."
The analysis of the various paintings also shows da Vinci
was constantly trying out new methods, Walter said. In the "Mona
Lisa," da Vinci used manganese oxide in his shadings. In others, he used
copper. Often he used glazes, but not always.
The results were published Wednesday in Angewandte Chemie
International Edition, a chemistry journal.
Tradition holds that the "Mona Lisa" is a painting
of Lisa Gherardini, wife of Florentine merchant Francesco del Giocondo, and
that da Vinci started painting it in 1503. Giorgio Vasari, a 16th-century
painter and biographer of da Vinci and other artists, wrote that the
perfectionist da Vinci worked on it for four years.
