An Italian art historian claims that the female model in the famous Leonardo da Vinci painting is, in fact, not a female at all.
According to researcher Silvano Vinceti, the figure in the painting is strongly reminiscent of Gian Giacomo Caprotti, a fellow also known as Salai, who apprenticed with Leonardo beginning in 1490. (The portrait is believed to have been painted during the early 1500s.)
But the books are hardly closed on this one. Arguably the world's most famous painting, "Mona Lisa" is also without question among the art world's most mysterious and debated works.
Here are a few other theories that have swirled around the "Mona Lisa" over the years.
1. Not only a man, but da Vinci himself
In January 2010, a group of art historians and anthropologists sought to exhume the great Italian painter to construct a virtual and then physical re-creation of his skull, which would then be compared to the painting and offer a verdict on the self-portrait theory.
2. La Gioconda
Other art historians propose that, based on information contained in Giorgio Vasari's mid-16th century Leonardo da Vinci biography, the painting is of Madam Lisa Giocondo, the wife of a wealthy Florentine.
3. The real da Vinci code?
Although the characters are invisible to the naked eye, scientists using highly magnified images of the "Mona Lisa" have identified small letters in her eyes, including the initials LV -- Leonardo da Vinci? -- in her right pupil.
Believe it or not, one of the primary mysteries that has consumed scholars of the painting for many years is the question of why the "Mona Lisa" appears to be lacking eyebrows and eyelashes. French engineer Pascal Cotte has even designed his own ultraviolet and infrared camera in his attempts to discover "only one hair."
5. Check those cholesterol levels
Dr. Vito Franco, professor of pathological anatomy at Palermo University, says that regardless of who the model is, "she shows clear signs of a buildup of fatty acids under the skin, caused by too much cholesterol," according to the BBC.
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