Every year, six million visitors from throughout the world travel across continents to the Musée du Louvre in Paris to gaze in wonder at Leonardo Da Vinci's famous portrait, the Mona Lisa. An oil painting on poplar wood, the portrait took Da Vinci four years (1503–1506) to complete. For centuries afterwards, his talent and ingenuity sparked several debates and a multitude of theories in a global effort to uncover the mysteries hidden behind the Mona Lisa's smile.

Who is Mona Lisa?

Many questions arose over the years as to the true identity of the lady in the portrait. The Italians call her La Gioconda, which means 'the light-hearted woman'. The French version, La Joconde, carries a similar meaning, provoking many thoughts and theories about the Mona Lisa's smile.

One popular theory suggests that the lady is the Duchess of Milan, Isabella of Aragon. Da Vinci was the family painter for the Duke of Milan for 11 years and could very well have painted the Duchess as the Mona Lisa. Other researchers have stated that the painting could depict a mistress of Giuliano de' Medici, who reigned in Florence from 1512 to 1516. A more recent thought by Dr. Lillian Schwartz of Bell Labs is that the Mona Lisa is the feminine version of Da Vinci himself. Through digital analysis, she discovered that Da Vinci's facial characteristics and those of the Mona Lisa are perfectly aligned with one another.

Despite the above theories, it is currently widely accepted that the portrait depicts Lisa Gherardini, the third wife of a wealthy Florentine silk merchant named Francesco del Giocondo. In fact, the title Mona Lisa is discussed in Da Vinci's biography, written and published by Giorgio Vasari in 1550. Vasari pointed out that Mona is commonly used in place of the Italian word Madonna, which could be translated into English as 'Madam'. Hence, the title Mona Lisa simply means 'Madam Lisa'.

How does she smile?

Mona Lisa's enigmatic smile has been the source of inspiration for many and a cause for desperation in others. In 1852, Luc Maspero, a French artist, jumped four floors to his death from a hotel room in Paris. His suicide note explained that he preferred death after years of struggling to understand the mystery behind Mona Lisa's smile. Today, visitors to the Musée du Louvre grapple with the same question: how does she smile?

Italians respond to this query by referring to a painting technique called sfumato, which was developed by Da Vinci. In Italian, sfumato means 'vanished' or 'smoky', implying that the portrait is ambiguous and blurry, leaving its interpretation to the viewers' imagination. This technique uses a subtle blend of tones and colors to produce the illusion of form, depth, and volume.

Dr. Margaret Livingstone, a neuroscientist at Harvard, explains that the human eyes consist of two regions – the fovea, or central area, and the surrounding peripheral area. The fovea recognizes details and colors and reads fine print, while the peripheral area identifies shadows, black and white, and motion. When a person looks at the Mona Lisa, the fovea focuses on her eyes, leaving the peripheral area on her mouth. Since peripheral vision is less accurate and does not pick up details, the shadows in Mona Lisa's cheekbones augment the curvature of her smile.

However, when the viewer looks directly at the mouth of the Mona Lisa, the fovea does not pick up the shadows, and the portrait no longer appears to be smiling. Therefore, the appearance and disappearance of Mona Lisa's smile is really an attribute of viewers' vision. In spite of the many revelations from years of research, the Mona Lisa remains an enigma today. The brilliant strokes of Da Vinci's paintbrush have ensured that she continues to evoke wonder, admiration, and inspiration in all who lay eyes upon her.