Laser scans Mona Lisa’s smile for secrets

Ottawa – Formerly unknown details about how the Mona Lisa wore her hair and covered her dress have literally come to light, thanks to a high tech analysis by Canadian and French researchers working on Leonardo da Vinci’s masterpiece.

The light was generated by a 3-D colour laser scanner designed and built at the National Research Council’s Institute for Information Technology. This equipment uses triangulation to create three-dimensional images with a depth resolution of 10 microns, just a fraction of the width of a human hair.

When the scanner is applied to a painting, the resulting digital model reveals visual details that can elude the sharpest eye, as well as information about the deposition of paint and the integrity of the underlying structure. The technical and aesthetic significance of such information highlighted an announcement held at NRC’s headquarters.

In the case of the Mona Lisa, the technique has revealed that the model was wearing a bonnet on her head, a common style for the time but an adornment that could not be seen with the naked eye. Similarly invisible is a thin gauze veil over her dress, typically worn by women who had recently given birth, which historians know she had done.

These subtle aspects of the 500-year-old portrait were obscured when a dark varnish was placed over its surface during the 19th century, likely the work of some well-intentioned conservator attempting to prevent the artwork’s deterioration. The scanner penetrated this layer to reveal the most intimate dimensions of the painting’s physical substrate, allowing these features to be viewed once again.

NRC offers samples of these various “looks” for the Mona Lisa, where visitors can witness the range of information about that painting that has now become available.

“You can see details on this image that you cannot see if you were to go to see the Mona Lisa in the Louvre today,” says John Taylor, one of the lead scientist in the NRC team that carried out the work. That team worked closely with members of the Centre de recherche et de restauration des musées de France, that country’s foremost art conservation authority.

Working under high security during two evenings when the Louvre was closed to the public, these experts were allowed to work directly with the priceless painting. Mounting the scanner on a high-precision platform just a few centimetres from the surface, the laser acquired successive bands four centimetres wide, with a lateral resolution of 60 microns.

A masterpiece

NRC has been honing this technology for 20 years, working with museums and other heritage institutions around the world.

In addition to domestic organizations like the Canadian Museum of Civilization and the National Gallery, such work has also been conducted with American and European Universities, the British Museum, and the Peabody Museum. More recent applications have extended to archeological sites, seeking to preserve information from deteriorating cave paintings found in Italy, as well as Chinese artifacts that are going to be lost due to flooding caused by the Three Gorges Dam.

Taylor noted that the work on the Mona Lisa represented the most ambitious application yet for this technology. The findings have become the basis of a book, Mona Lisa: Inside the Painting.

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