GENEVA -- The mystery behind the most enigmatic smile in art -- Leonardo da Vinci's "Mona Lisa" -- just got a little more complicated.
In a coming-out party of sorts in Geneva, rounds of flashbulbs popped Thursday as the nonprofit Mona Lisa Foundation pulled back the curtain to present what it claims is a predecessor of the world's most famous portrait.
But even the experts brought in by the foundation weren't sure about that claim just yet.
The art world is prone to all sorts of rumors and speculation -- and, periodically -- discoveries that jolt accepted norms. Two years ago, a retired French electrician claimed that he had turned up 271 Picasso works that had been sitting for decades in his garage -- and Picasso's heirs claimed theft.
But a new claim about the world's most famous painting, which draws millions of visitors to Paris' Louvre Museum each year, resonates like a thunderclap in the art world. It also prompts a new look at a painting that all by itself still raises a lot of questions for experts -- not least the timeless "Is she smiling or not?"
The "Isleworth Mona Lisa" features a dark-haired young woman with her arms crossed against a distant backdrop. The foundation insists it's no copy but an earlier version of the Louvre masterpiece.
At the presentation, Alessandro Vezzosi, director of the Museo Ideale Leonardo da Vinci, said the painting was intriguing but needs further study. He declined to line up behind the foundation's claims that it was truly a "Mona Lisa" predecessor painted by da Vinci.
"The Isleworth Mona Lisa is an important work of art deserving respect and strong consideration -- as well as a scientific, historic and artistic debate among specialists rather than a purely media interest," he said.
"Scientific tests don't demonstrate the authenticity (and) the autography of a painting, but demonstrate it's from a certain era, whether the techniques are similar or not," Vezzosi told The Associated Press in French. "Here, there are many open questions," before waving his hand over the painting, as a security guard with folded arms stood nearby.
Ever since the 16th century, several historical sources suggest that da Vinci painted two "Mona Lisa" versions. One was of Mona Lisa Gherardo around 1503 that was commissioned by her husband, Francesco del Giocondo, the foundation said. Another -- the one in the Louvre -- was completed in 1517 for Giuliano de Medici, da Vinci's patron. That theory fits with da Vinci's tendency at times to paint two versions of some of his works, like the Virgin of the Rocks, the group said.
Foundation members say it's unrealistic to think that the woman sat twice for a portrait, but that the meticulous, mathematical approach suggested that da Vinci may have projected in his mind what she would have looked like between the first alleged "Mona Lisa" and the "Mona Lisa" in the Louvre.
However, the foundation acknowledged that the "Isleworth Mona Lisa" remains unfinished, and that da Vinci didn't paint all parts of the work. Still, the group pointed to newly discovered evidence in 2005 from Heidelberg, Germany, that suggested da Vinci was working on at least the head of such a painting in 1503.
The painting has been in headlines before, starting in the early 20th century. And it's not unknown to a foreign audience: It was shown in Japan last year before the foundation's research was finished.
Experts say Thursday's unveiling was designed to draw more attention and scrutiny from worldwide art experts about whether it's authentic: A start more than a finish.
The Isleworth painting first came to public light after British art collector Hugh Blaker found it in the home of a nobleman in Somerset, England before World War I, said Robert Meyrick, head of the art school at Wales' Aberystwyth University.
Blaker bought the painting and took it to his private studio in Isleworth outside London. U.S. and British newspapers, meanwhile, speculated even then that it might be a da Vinci. But at that time only art experts -- not high-tech science tests like the ones conducted by the foundation -- could judge its possible bona fides.
During World War I, Blaker shipped the painting to Boston's Museum of Fine Arts for safekeeping, the foundation said. In 1962, it was bought by U.S. collector Henry Pulitzer. When he died in 1979, his reported mistress -- Elisabeth Meyer -- inherited it, but it remained in a Swiss bank vault.
After she died, an "international consortium" -- which the foundation declined to identify -- bought the painting in 2008, according to the group's chronology. The foundation was set up two years later, determined to try to show that it was a real da Vinci.
The Mona Lisa Foundation's members are more from the business world than the art world. Participating in Thursday's show was David Feldman, an Irish-born stamp auctioneer; his brother Stanley, an art historian who was the main author of an extensive book on the "Isleworth Mona Lisa"; and Markus Frey, a lawyer in Zurich who is the foundation's president.
"It is the ultimate goal of our endeavors to give that stunning earlier version the place in art history which it deserves, after such a long period in obscurity," Frey said. "This great piece of art must finally be given to the public eye."
He said viewers can draw their own conclusions.
"Quite a few things we were taught in our early school years turned out to be incorrect, or were overturned by new discoveries or updated information," he said.
"The quintessence of any humanistic education is to ask questions, to be inquisitive, and to challenge authority. Of course, authority often sits in an ivory tower, which will no doubt be our biggest challenge."
The foundation and its backers paid "several million" to conduct research tests -- forensic analysis, carbon-dating and computerized regression analysis -- on the work, David Feldman said. He wouldn't say how much the painting was bought for in 2008.
Carlo Pedrotti, one of the world's most eminent scholars on da Vinci, hailed the foundation's "extraordinary contribution to scholarship."
In a letter to the foundation presented Thursday, Pedrotti called the group "precisely the sort of research institute, if not a veritable investigating agency -- an FBI for Leonardo studies! -- that I had always hoped for."
Martin Kemp, a da Vinci scholar and Oxford University professor, said he hadn't seen the painting but doubts that it is authentic. He cautioned that the foundation might have its judgment clouded by a possible payoff.
"If this were the original version of the most famous picture in the world, heaven knows what it would cost -- a lot of money," he told APTN in an interview at his home near Oxford. "You'd probably be on your way to 200 million pounds ($325 million) or to stratospheric realms."
"There are big, big stakes involved, and people become committed to it," he noted.
Still, who wouldn't want to have their own "Mona Lisa?"
"Having a Leonardo is a very sensational thing to have," Kemp admitted. "If I had a Leonardo, it would secure my fame forever."