When is a Vermeer Not a Vermeer?

Johannes Vermeer of Delft left behind fewer than 50 paintings when he died aged 43 in 1675. Those that survived have beguiled art lovers for more than a century: intimate domestic scenes, such as a girl reading a letter at an open window, or a maidservant absorbed in pouring milk, bathed in soft, gentle light. As Vermeer’s output was so small, it is an event when a painting is declared to be by his hand. But there are few precedents for a recent tussle over the artist. One painting has been declared definitively “a Vermeer” by one museum, while another has downgraded it.