Over the past month, scientists at the Louvre have been carefully examining a 16th-century charcoal drawing of a nude woman known as Monna Vanna, long attributed to the studio of Leonardo da Vinci. They wondered if, perhaps, there is a closer relationship between this half-smiling nude and the most iconic portrait of all time than experts long supposed.

Since 1862, the Monna Vanna drawing has quietly lived in the collection of Renaissance art at the Conde Museum, located in the palace of Chantilly, north of Paris.