Mona Lisa’s Smile

Mystery of the Mona Lisa’s smile solved: Second painting shows how da Vinci created an optical illusion to trick viewers

The Mona Lisa's mysterious expression may have captivated the world, but hers isn't the only enigmatic smile Leonardo da Vinci created.

Researchers examining an earlier painting by the Renaissance master claim to have unravelled the painter's secret to creating an 'uncatchable smile'. 

The study reveals how La Bella Principessa (right), painted by da Vinci before the Mona Lisa (left) in the late 15th Century, uses a clever trick to lure in the viewer. 

Researchers found that by expertly blending colours to exploit our peripheral vision, the shape of the subject's mouth appears to change according to the angle it is viewed from.

When viewed directly, the slant of the mouth is distinctly downwards, according to the research.

As the viewer's eye wanders elsewhere to examine other features, however, the mouth appears to take an upward turn, creating a smile that can only be seen indirectly, much like the Mona Lisa's.

The technique is called sfumato, and can be seen in both the Mona Lisa and La Bella Principessa.
'As the smile disappears as soon as the viewer tries to 'catch it', we have named this visual illusion the 'uncatchable smile,' researchers wrote in a paper published in the journal Vision Research.

And while other artist's have attempted to use the same technique,  none have done so as expertly as da Vinci, the researchers claim.

To find out how da Vinci's illusions worked, the researchers set up test in which people either viewed the portraits from a distance or saw blurred versions, according to a report in Discover magazine.

The researchers used a series of experiments to examine how different points of view and levels of blur in the images themselves could alter a viewer’s perception.

First they conducted a number of tests to see how a viewer’s distance from the portrait would influence their perception.

They found that when viewed from further away, both the Bella Principessa and Mona Lisa appeared to be smiling more than the portrait by del Pollaiuolo.

They also used digital manipulation to alter the level of flur in each of the paintings. They found as blur in the two da Vinci paintings was increased, the smiles appeared to increase.

The researchers asked volunteers to view digitally manipulated versions of three paintings - da Vinci's La Bella Principessa (top), Mona Lisa (middle) and Portrait of a Girl by Piero del Pollaiuolo (bottom). They changed the level of blur in the paintings to examine whether this changed the impression of a smile.

When viewed directly, the slant of the mouth in the Mona Lisa (pictured) is distinctly downwards.  But as the eye moves elsewhere to examine other features, the mouth appears to take an upward turn, creating a smile that can only be seen indirectly

In del Pollaiuolo’s painting the perception of the girl’s smile remained broadly the same, and actually decreased slightly as the blur worsened.

This suggests da Vinci’s technique specifically relies upon the viewer seeing the mouth with unfocused eyes in order for the smile to appear.

In a final experiment, the researchers tested whether the mouth or the eyes were responsible for the mysterious smile illusion by masking the features with black rectangles.

They found when the mouth was obscured, the illusion did not appear to work, but when the eyes were obscured, viewers still detected the hint of contentment in La Bella Principessa’s smile. 

Soranzo told Discover, 'Given da Vinci's mastery of the technique, and its subsequent use in the Mona Lisa, it is quite conceivable that the ambiguity of the effect was intentional.'

By ELLIE ZOLFAGHARIFARD FOR DAILYMAIL.COM