[...] 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 Salaì and Francesco Melzi, and other imitators of the Florentine’s style. [...]

Until now the Condé 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 Salaì 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 Condé 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.