“My heart will always pound when I think about that drawing,” Dr. Bambach said. “It has so many changes of ideas, so much energy in the way he explores the figure. It has a furious spontaneity.”

“It’s like glancing over his shoulder,” she said of Leonardo.



Dr. Bambach estimates the drawing’s date at 1482 to 1485, during the early phase of Leonardo’s period in Milan, when he painted his first version of “The Virgin of the Rocks,” now in the Louvre.

(The Met said it had no agreement with the auction house to buy or to show the artwork.)

According to Dr. Bambach, the drawing — which she hopes will be bought by a French museum — represents the first “Leonardo, full stop” discovery (as she put it) in this medium since 2000, when Sotheby’s in London offered a slighter sheet from around 1506 to 1508 that had black chalk and pen studies of Hercules and whirlpools. It failed to sell against a low estimate of 400,000 pounds, or what was then about $600,000, but sold later for about $550,000. The drawing (also attributed by Dr. Bambach) is now jointly owned by the Metropolitan Museum of Art and the New York collector Leon Black and his wife, Debra Ressler.

As for a much-debated mixed-media profile portrait of a young woman, known as “La Bella Principessa,” which eight years ago was valued by the London dealer Simon Dickinson at as much as $150 million, Dr. Bambach commented, “It does not look like a Leonardo.”