A DRAWING of a young woman bought at auction for £11,000 and thought to be the work of an unknown artist has been attributed by several experts to Leonardo da Vinci, sending its potential value rocketing to £100m or more.

If confirmed, it would be the first work to be attributed to Leonardo since the Lady with an Ermine was identified as his work in the early 19th century.

A Swiss-based collector, who is insisting on anonymity, bought the drawing, entitled Head of a Young Girl in Profile, at Christie’s in New York in 1998. It was catalogued as “German school, early 19th century”, by the auction house.

The collector bought it on a whim. “He thought it was a nice, pretty thing,” said his friend Peter Silverman, a Canadian collector. The owner kept the work unframed in a drawer at his home.

Silverman was the first to spot Leonardo’s hand in the drawing when the owner, who was showing him his collection last year, pulled it out of the drawer.

“My heart started to beat a million times a minute. I immediately thought this could be a Florentine artist. The idea of Leonardo came to me in a flash,” Silverman said.

Silverman sent a photograph to Dr Nicholas Turner, former curator of drawings at both the British and Getty museums. “At first I thought of two possibilities: a very beautiful fake, or an unknown Leonardo,” Turner said.

He was struck by the skill of the shading around the face, which he believes could have been drawn only by a left-handed artist such as Leonardo. “At the time, apart from Vinci, only two or three artists painted with their left hand with such dexterity,” he said.

Silverman made an appointment to see experts from Lumière Technology, a Paris-based company that specialises in digital images of fine art. He drove there on his scooter with the drawing perched on the back in a briefcase.

They used scanning technology to look at the brush strokes behind a heavy-handed 19th century restoration. The experts reported back: “You’ve got a Leonardo da Vinci.”

The drawing, of black, red and white chalk and watercolour, may portray the Lombardi aristocrat Bianca Maria Sforza shortly before her marriage to Emperor Maximilian I. Leonardo travelled with the newly weds across the Alps to the Tyrol.

“We found one striking parallel with Lady with an Ermine – a very rare touch – the artist drew the eyelashes both above and under the eye,” said Pascal Cotte, Lumière’s research director. Carbon dating of a section of the parchment that had been left untouched by the artist is due to be completed by September. Silverman expects an auction house to guarantee a price of at least £50m if the attribution is confirmed and the owner decides to sell. Other experts said the value could be as high as £100m.

It would be the first work on parchment attributed to Leonardo. Several of his friends in Florence and Milan used this medium, and he himself recommended it in his Treatise on Painting.

Further backing for the attribution came from Mina Gregori, an authority on Florentine paintings, and Cristina Geddo, an expert on the Leonardo school. Geddo said the sitter’s hairstyle, with the hair braided into a single plait, and details known as “Leonardesque knots” on the border of her dress tie it “securely” to his time in Milan in the late 15th century.

Alessandro Vezzosi, director of the Museo Ideale museum in the artist’s birthplace of Vinci, near Florence, has included the work in his monograph Leonardo Infinito, published this month.

Vezzosi said the drawing may have been “a commission for a marriage proposal made from afar, to emphasise the beauty of the bride-to-be”.

Professor Carlo Pedretti, the world’s leading expert on Leonardo, is more cautious. He said he would wait for further laboratory tests to date the parchment and the drawing materials. He added: “Notwithstanding the questions raised by the lack of any known earlier provenance, this work constitutes – at least for the moment – the most important discovery since the early 19th-century re-establishment of the Lady with the Ermine as a genuine work by Leonardo.”

Suddenly aware of its potentially astronomical value, the owner is now keeping the drawing in a safe.

“He wants to stay anonymous, because he doesn’t want to pay sky-high insurance on it,” said an acquaintance.

“He was originally going to give it to his daughter as a wedding present, though now he has changed his mind.”

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