年轻未婚妻的肖像

This chalk-and-ink profile of a young woman on vellum, dressed in the Milanese fashion of the 1490s, is one of the most argued-over drawings of recent decades. Some scholars, led by Martin Kemp, put it in the hand of Leonardo da Vinci and identify the sitter as Bianca Sforza, a daughter of the Duke of Milan. Most experts do not accept that. In 1998 it was even catalogued as the work of a 19th-century German artist, before radiocarbon tests pushed the vellum itself much earlier and reopened the question. It has never entered a public museum; it sits in a Swiss vault, its name and its maker still unsettled.