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.

Next week a wooden object 502 years old, inventory number 779, will be moved to a new location in the largest art museum in the world. The object is a small portrait of an obscure Florentine ...