A French art expert believes a charcoal drawing kept in a collection for more than 150 years may be a preparatory sketch made by Leonardo da Vinci of the Mona Lisa.
The black-and-white drawing of a woman, nude from the waist up, known as the Monna Vanna, was previously attributed to Leonardo's studio, suggesting it was done in his style by a pupil or follower, not by the master himself.
But after preliminary tests at the Louvre Museum, experts believe the sketch may well have been drawn by Leonardo.
Among the signs, according to curator Mathieu Deldicque, are the fact the drawing was made during the same period as the Mona Lisa, the paper is from the same region of Italy, and the technique is very similar to that of the Mona Lisa.
"For the moment we know that the paper on which this (sketch) is drawn was dated from the time of Leonardo da Vinci ... that is to say the beginning of the 16th century," Deldicque said in an interview Friday with The Associated Press. "We know that this paper comes from Italy, between Venice and Florence, so it is similar."
Imagery picked up other signs that may point to a sketch by Leonardo despite its "very worn elements," he said, noting the "quality" of the face and arms, which recalls the master.
"The position of the arms is very important because it is literally (like) the position of the arms of the Louvre painting," Deldicque said.
Among the array of clues under study is whether the artist of the sketch was left-handed.
"We know that Leonardo da Vinci was left-handed and now we are just looking for the left-handed features," the curator said. But the task is difficult. "The drawing is very old, very fragile," he said, making it uncertain firm evidence will be uncovered showing that the charcoal nude was sketched with a left hand.
Leonardo, who lived from 1452 to 1519, was an engineer, scientist, inventor and sculptor, as well as one of the finest artists of the Italian Renaissance.
He painted the Mona Lisa, also known as La Gioconda and regarded as the world's most valuable artwork, at the beginning of the 16th century. It is believed to depict Lisa Gherardini, the wife of a successful merchant.
The charcoal portrait, in which the woman is holding a similar pose to the Mona Lisa but with her body more side-on and her head turned further over her left shoulder, has been held in a collection at the Conde Museum at the Palace of Chantilly, north of Paris, since 1862.
Deldicque said that while it was exciting to think the charcoal drawing was created by Leonardo, there were more tests to be done.
"We have one more month of analysis and then a very slow process of history of art with a collection of analysts and advice by specialists," he said.
It is possible that process will determine that the authorship is the same. But it may also be inconclusive, he said, adding: "Maybe the mystery will remain."