For over 250 years, Vermeer’s Girl Reading a Letter at an Open Window (circa 1659) has resided quietly at the Dresden Gemäldegalerie, where it attracts viewers from all over the world. A solitary young woman reads intently in front of an open window, an ochre wall rising behind her. It turns out, however, that the painting has been keeping a secret. Previous X-ray examinations discovered a concealed depiction of Cupid on that ochre wall. But was it painted over by Vermeer, or later on by someone else? With new laboratory testing, experts determined that the paint-over was not done by Vermeer. The work has now been restored to its original state, and this exhibition unveils the new “painting within a painting.” The presence of Cupid, of course, allows us to “read” the painting—the letter!—more pointedly. Other works by the Dutch master are also on view. —E.C.