A Swiss foundation claims new technology proves a painting known as the Isleworth Mona Lisa is an image of the same woman shown in the Louvre, but painted at an earlier date by the same artist – Leonardo da Vinci.

The Mona Lisa Foundation in Zurich exists solely to prove that Leonardo’s earlier version of the Mona Lisa “known and loved in its own right, as much as the version that hangs in the Louvre Museum,” according to a statement on its website.

Both images are believed to be of Lisa Del Giocondo, wife of a wealthy Florentine merchant and both depict her with an enigmatic smile.

The Isleworth Mona Lisa has been known to experts for years, but they remain divided on whether the painting is by Leonardo or whether it shows the same woman.

Scientific tests

"So far, not one scientific test has been able to disprove that the painting is by Leonardo," said art historian Stanley Feldman, author of a foundation-sponsored book entitled Mona Lisa: Leonardo's Earlier Version released Thursday. "We have used methods that were not available to Leonardo 500 years ago."

The painting was tested via gamma rays and infrared reflectography, according to the foundation. Testing proved the painting dates from the 16th century and that the pigments used were consistent with those used in other Leonardo paintings.

The Isleworth Mona Lisa is larger than the painting in the Louvre and more brightly coloured, with a different background. However the posture of the woman and her clothing are similar.

Stanley Feldman, art historian, poses in front of a painting attributed to Leonardo da Vinci, called the Isleworth Mona Lisa. (Denis Balibouse/Reuters)

"When we do a very elementary mathematical test, we have discovered that all of the elements of the two bodies — the two people, the two sitters — are in exactly the same place," Feldman said.

"It strikes us that in order for that to be so accurate, so meticulously exact, only the person who did one did the other ... It's an extraordinary revelation in itself, and we think it's valid."

There are also written accounts from the 16th century that speak of Leonardo’s practice of doing two or more versions of a single painting, and of two paintings of a certain Florentine lady, one of which remained unfinished. The Isleworth Mona Lisa is unfinished.

The foundation argues Leonardo did two paintings from the same sitting, but completed only a later version, which now hangs in the Louvre.

London art dealer discovers it

The earlier painting was in the collection of a British family, living in Somerset, for about 150 years. It was purchased just before the First World War by London art dealer Hugh Blaker, who sent it to the U.S. for fear London would be bombed. It remained safely in the collection of a Boston museum until 1922, when Blaker sent it to Italy to be verified as a true Leonardo.

At that time, art experts, relying on their familiarity with the work of the great master, supported his theory it was an earlier version of the Mona Lisa.

According to the Mona Lisa Foundation, the painting was then bought by Henry Pulitzer, who put it in a Swiss bank vault before his death in 1979. There it languished for 40 years, until the foundation was formed in an effort to raise the profile of the Isleworth Mona Lisa.

The foundation has released a video, scientific data and details of the supporting historical evidence online. However there are many skeptics.

Martin Kemp, an Oxford University professor and Leonardo expert, said it is more likely the painting is a copy by another painter who admired Leonardo’s work.

"The Isleworth Mona Lisa miss-translates subtle details of the original, including the sitter's veil, her hair, the translucent layer of her dress, the structure of the hands ... " Kemp said.

"The landscape is devoid of atmospheric subtlety. The head, like all other copies, does not capture the profound elusiveness of the original."

With files from The Associated Press