The National Gallery has opened the first-ever survey of the paintings of Jan Lievens, who launched his career alongside Rembrandt in Leiden. Constantine Huygens even commissioned the two men to paint the same subjects in a sort of competition. Blake Gopnik finds that, “[j]udging by this show, the almost unknown test-pictures by Lievens aren’t obviously weaker than the very famous versions Rembrandt came up with.”