New tests on a painting billed as the original version of the Mona Lisa have produced fresh proof that it is the work of Leonardo, a Swiss-based art foundation has said.
The tests on his 15th century portrait were carried out by a specialist in "sacred geometry" and by the Swiss Federal Institute of Technology in the wake of the Geneva unveiling of the painting, the Isleworth Mona Lisa, last September.
"When we add these new findings to the wealth of scientific and physical studies we already have, I believe anyone will find the evidence of a Leonardo attribution overwhelming," said David Feldman, vice-president of the foundation.
The Mona Lisa in the Louvre for over three centuries has long been regarded as the only one painted by Leonardo, although there have been copies, and claims for the Swiss-held one were dismissed by some experts last year.
But it also won support in the art world, encouraging the Zurich-based Mona Lisa Foundation – an international group that says it has no financial interest in the work – to pursue efforts to demonstrate its authenticity.
Feldman, an Irish-born international art and stamp dealer, said he was contacted after the public unveiling of the portrait – which shows a much younger woman than in the Louvre – by the Italian geometrist Alfonso Rubino.
"He has made extended studies of the geometry of Leonardo's Vitruvian Man [a sketch of a youth with arms and legs extended] and offered to look at our painting to see if it conformed," said Feldman.
The conclusion by the Padua-based Rubino was that the Isleworth portrait – named after the London suburb where it was kept by the British art connoisseur Hugh Blaker 80-90 years ago – matched Leonardo's geometry and must be his.
The Zurich institute carried out a carbon-dating test on the canvas of its painting and found that it was almost certainly manufactured between 1410 and 1455, refuting claims that it was a late 16th century copy.