The Mona Lisa isn’t just the most famous painting of Leonardo da Vinci's—it’s arguably one of the most well-known works of art ever created. Many credit the otherwise simple portrait’s immense fame to her mysterious smile. When viewed head-on her smile softens, but when looked at from an angle the smirk becomes more pronounced. This has long been accepted as one of the art world’s greatest mysteries, but researchers from Sheffield Hallam University think they’ve finally homed in on a possible explanation. 

By studying La Bella Principessa, a newly discovered portrait many experts attribute to da Vinci, researchers believe they may have found the secret to Mona Lisa's unique expression. The Mona Lisa and La Bella Principessa showcase a painting technique known as “sfumato” which employs subtle colors and shading around the subjects' mouths. This creates an optical illusion that toys with the viewers' direct and peripheral vision. When focusing on the eyes of the subject it appear as if she’s smiling, but staring at the mouth directly makes the smile suddenly disappear.

The researchers, Michelle Newberry and Alessandro Soranzofurther supported their theory by showing participants digital copies of the paintings from different distances and angles as well as ones that had been blurred to varying degrees. The blurrier and the farther away the paintings were, the more likely the viewers were to recognize the smiles. 

For fans of Leonardo da Vinci–related mysteries, it looks like this case may have been solved. As for what's causing Mona Lisa's mischievous smirk in the first place, that's a different story.

[h/t: Calgary Herald]