More than half a century ago, a young librarian wandered inside a small London antique shop. There, amongst vintage furniture and porcelain vases, was a stern, elderly woman in a black nun’s habit. She stared him down from an elaborate wooden frame. Believing the painting to be an unknown artist’s copy of Anthony van Dyck’s “Portrait of Infanta Isabella Clara Eugenia,” Chris Wright, the librarian, bought the painting of the “bad-tempered old lady,” for £65 (about $88), the equivalent of about three weeks’ wages. For decades, she hung above his…
