Have researchers unlocked the mystery of Mona Lisa’s famously enigmatic smile?

Researchers from a British university believe they have unlocked the mystery of the Mona Lisa’s famously enigmatic smile – by analysing another, recently-discovered masterpiece by Leonardo da Vinci.
By looking at La Bella Principessa, the portrait of the daughter of a Milanese nobleman, researchers found intriguing clues as to how the Renaissance genius managed to paint the Mona Lisa in such a way that her coy smile appears most pronounced when viewed from an angle and less so when looked at directly.
The researchers, from Sheffield Hallam University, believe that in the case of both portraits, the same effect was created by a painting technique known as “sfumato”, meaning soft or pale in Italian, in which subtle colours and shades around the mouths of the subjects create a clever optical illusion.
If one focuses on the eyes of the subject, the lips appear to slant delicately upwards in a tentative smile, but if one looks at the mouth directly, they appear flatter.
In both paintings, Leonardo expertly exploited differences between our peripheral vision and direct sight.
The research suggests that the Mona Lisa’s dancing smile was no fluke, but a deliberate technique by Leonardo that he had already perfected in La Bella Principessa, an earlier work.
“As the smile disappears as soon as the viewer tries to ‘catch it’, we have named this visual illusion the ‘uncatchable smile’,” wrote the researchers, Michelle Newberry and Alessandro Soranzo, from Sheffield Hallam University.
They organised a series of experiments in which people were asked to look at the Mona Lisa and La Bella Principessa from different distances and angles.
They were also shown digital copies of the paintings which had been blurred to different degrees.
The blurring mimicked the effects of people’s peripheral vision, in which objects are seen less distinctly. The more blurred the images were, the more Leonardo’s subjects appeared to smile.
“La Bella Principessa’s mouth appears to change slant depending on both the viewing distance and the level of blur applied to a digital version of the portrait,” they wrote in a paper published by the journal Vision Research.
“Through a series of psychophysics experiments, it was found that a perceived change in the slant of La Bella Principessa’s mouth influences her expression of contentment.”
The volunteers involved in the experiments said that both the Mona Lisa and La Bella Principessa appeared more smiley when viewed from a distance or when their portraits were slightly blurred.
The scientists also showed the people in the tests images of the two women with their mouths or eyes blacked out.
In the images with the mouths obscured, the volunteers reported that they could discern no change of expression in the portraits, suggesting that the key lay with the mouths.
Leonardo painted La Bella Principessa, known in English as Portrait of a Young Fiancee, before he started work on the Mona Lisa.
It was long thought to have been the work of an early 19th-century German artist, but in recent years has been attributed to Leonardo by leading art historians, including Martin Kemp, a Leonardo expert at Oxford University.
The “beautiful princess” of the title is Bianca Sforza, the illegitimate daughter of Ludovico Sforza, one of the dukes of Milan during the late 15th century.
The portrait was commissioned in 1496 when she was 13, on the eve of her marriage to a general in the Milanese army.
Within months of her marriage she was dead, possibly as a result of complications arising from an ectopic pregnancy.
The model for Mona Lisa is thought by many scholars to be Lisa Gherardini, the wife of a rich Florentine silk merchant.