Wearing just a smile . . . Leonardo’s lost Mona Lisa

The story of the topless Mona Lisa is almost as enigmatic as her smile. According to his contemporaries, Leonardo da Vinci produced a nude version of his masterpiece that vanished two years after his death in 1519.

Now, researchers at the Louvre in Paris believe that a charcoal impression of Mona Lisa that has long been attributed to students of the renaissance artist, could be the work of the master himself.

Leonardo’s topless variant of La Joconde (Mona Lisa) is believed to have inspired several nude portraits. These works, also known as Mona Vannas, are attributed to Leonardo’s pupils Salai and Francesco Melzi, and other imitators of the Florentine’s style.

Until now the Conde museum in Chantilly has described its charcoal Joconde Nue, which was brought to France by Joseph Fesch, Napoleon’s ambassador to the Vatican, as "the work of Salai or Melzi, inspired by a lost painting by da Vinci".

However, new scientific analysis suggests it is an earlier work than previously thought. Mathieu Deldicque, curator of the Conde museum, said that analysis of the drawing was still taking place at the Louvre’s centre for research and restoration but it showed that the work probably came from Leonardo’s workshop and raised the possibility that he drew it.

"It’s possible, though there’s no certainty, that this was the preparatory drawing for the painted Joconde nue," he told The Times.

"We don’t even know if that portrait was really painted but there’s a strong probability that it was. What has tipped us off are retouches. There are little clues."

These include a watermark in the paper and dating analysis that places the paper and materials in the first decade of the 16th century.

"What’s new is that we have been able to narrow down a time frame and an artistic environment and we have found the quality to be very high," he said.

"The creative work on this oeuvre is very close to the lower part of the Mona Lisa, the one in the Louvre."

Tiny holes around the drawing show that it was used as the tracing of an oil portrait in the technique of Leonardo’s times.

Cross-hatching on the drawing had been produced by a righthanded artist while Leonardo was left-handed, but it could have been applied after the initial work, Mr Deldicque said.

Mystery about the portrait remains, he said.

"Is it really La Joconde. Is it a courtesan or even the goddess Flora or an allegory?" he said.

Experts have long speculated that Leonardo produced the Mona Vanna as a mocking version of his original masterpiece, whose sitter is traditionally identified as Lisa del Giocondo, the wife of a Florence merchant.

Leonardo’s Mona Vanna and its imitators are believed to have inspired Raphael’s 1513 Portrait of a young woman, a nude painting of his mistress.