The controversies around her smile and eyes have generated almost as much research and debate as the painting itself. Anyone who has seen Leonardo's Mona Lisa had the illusion that the Gioconda was staring at them irrespective of their angle. There have been numerous scientists who have attempted to deconstruct this particular aspect, and explain how human sight responds to Mona Lisa's eyes. For instance, Margaret Livingstone, a professor at Harvard University, has argued that the painting is most effective when viewed peripherally, and that Gioconda's smile is most striking when looking directly at her eyes. Contemporary response was not necessarily favorable to the painting as Leonardo's contemporaries did not consider the Mona Lisa Leonardo's most important work. Several accounts of Italian painting written during the artist's life or a little later, fail even to mention it. For instance, Paolo Giovio, writing shortly after Leonardo's death in 1519, simply states that he painted the portrait of Mona Lisa, "wife of Francesco del Giocondo, which was bought by King Francis I, it is said, for 4000 scudi." (Boas 212) In fact, during the sixteenth and seventeenth centuries, the only aspect which was truly interesting to critics and art commentators was the price of the painting which was considered immense for that period of time. The only relatively positive recorded comment on the Mona Lisa during the sixteenth century was that of Lomazzo who praised it along with portraits by Raphael and Andrea del Sarto as "peculiarly adapted to its subject." (Ibid) The most influential of earlier comments on the painting belonged to Italian painter Vasari who established a tradition as far as Mona Lisa criticism. It is not until the middle of the seventeenth century that the Mona Lisa is established as a true masterpiece. Pere Dan, who was in charge with making a catalogue of the artworks at Fontainebleau, called it "une merveille de la peinture" -- a miracle of painting (Boas 213).

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The artist placed his model in the middle of the painting, using a pyramid design in order to determine the exact center. There is also an important note to be made on the fold of Gioconda's hands that form the front of the pyramid whereas the glowing light on the model's chest, neck and face, it was used by Leonardo to create many of the geometric shapes -- mainly circles and spheres -- which make up the painting when the latter is deconstructed. The form of the painting itself is rather simple depicting a very popular theme during the time of its creation, i.e. A form of the Seated Madonna, invoked by many Renaissance painters. However, Leonardo modified this popular formula aiming to create mystery and a sense of distance between the model in the painting, and its audience. To create this feeling, he used the armchair that the Gioconda is sitting on. Although uncomplicated, the image evoked by the painting generates a very strong emotional response from the audience, and this response has everything to do with her famous smile. Everything surrounding her face is dark, so the light on her face is the element which attracts the eyes of the audience to her smile and her eye line. In fact, from this point-of-view, it is interesting to note that the mystery exuded by the Mona Lisa is created by the contrast between this natural attraction to the painting resulted from the usage of light and darkness, and the distance that the artist creates between the subject of his masterpiece, and its audience.
Sources

Annand Taylor, Rachel. Leonardo the Florentine: A Study in Personality. Richards Press, 1927.

Boas, George. "The Mona Lisa in the History of Taste." Journal of the History of Ideas 1.2 (1940): 207-224.

McCurdy, Edward. The Mind of Leonardo Da Vinci. Dodd, Mead, 1928.

Hegarty, Melinda. "Leonardo…