To add to the contradiction, the account of the Renaissance historian Gian Paolo Lomazzo (1538 – 1592) referred in his 1584 Treatise on Painting, to "a Gioconda and a Mona Lisa."
"The accounts are totally different from each other, and were written decades apart. Taken together, they point to two distinct and different portraits, one being of the young Mona Lisa, and the second to a 'Florentine woman,' or 'La Gioconda,'" the Mona Lisa Foundation said.
La Gioconda is the Italian alternative name for the Mona Lisa hanging in the Louvre.
"The historical evidence suggests that the earlier version of Mona Lisa, the portrait of Lisa del Giocondo, was probably delivered unfinished into the hands of her husband Francesco before Leonardo departed Florence for Milan in 1506," the Mona Lisa Foundation wrote.
Further historical evidence would come from a drawing by Raphael of the Mona Lisa. Now in the Louvre, the drawing was probably done from memory from Leonardo's original after Raphael visited the master's studio in 1504.
Featuring two columns, the sketch mirrors that of the Isleworth painting.
"The artwork indeed reminds Raffaello's drawing and raises many questions," Alessandro Vezzosi, the director of the Museo Ideale in the Tuscan town of Vinci, where Leonardo was born in 1452, said.
Along with leading Da Vinci expert Carlo Pedretti of the Armand Hammer Center for Leonardo Studies at the University of California, Vezzosi is carrying an independent research on the puzzling Isleworth painting.
He suggested that most likely several hands worked on the canvas.
"Just compare the face with its quality and intensity with the cluster of trees in the backdrop. The trees reveal a different technique and problems of perspective. Most likely, they were painted by someone else," Vezzosi said.
In the past twelve years, the painting underwent any possible test, from gamma rays and infrared reflectography to forensic age regression to determine what the Louvre Mona Lisa would have looked like 11 to 12 years earlier.
But it was mathematics that helped the foundation's experts to discover what they called "Leonardo's hidden technique."
Simple horizontal lines drawn across both the Louvre and the Isleworth paintings - previously brought to the same ratio - show exact proportional similarities despite the fact that, in reality, the figures within them were not painted to the same size.
"The eyes, the nose, the distance between the mouth and the chin, are exactly in the same location. Only the same artist could have known how to do that without the benefit of modern technological aids," art historian Stanley Feldman, principal author of the 320 page book, said.
As expected, the claim is raising a controversy in the art world.
Vezzosi called the suggestion that Da Vinci portrayed Lisa del Giocondo at two different moments of her life "a fascinating possibility," but according to Oxford professor Martin Kemp "there is no basis for thinking that there was an earlier portrait."
"The Isleworth Mona Lisa mistranslates subtle details of the original, including the sitter's veil, her hair, the translucent layer of her dress, the structure of the hands. The landscape is devoid of atmospheric subtlety," he said in a statement.
Kemp also pointed out that the Isleworth piece is painted on canvas.
Like the majority of Leonardo's works, the Mona Lisa in the Louvre is painted on wood.
Photos: Detail of the Isleworth Mona Lisa. Credit: The Mona Lisa Foundation.
– The Isleworth Mona Lisa. Credit: The Mona Lisa Foundation.
– A graphic experiment, comparing the earlier and Louvre Mona Lisas, shows exact proportional similarities. Credit: The Mona Lisa Foundation.