What's in a shadow? Menace, seduction, or salvation? Immaterial but profound, shadows lurk everywhere in literature and the visual arts, signifying everything from the treachery of appearances to the unfathomable power of God. From Plato to Picasso, from Rembrandt to Welles and Warhol, from Lord of the Rings to the latest video game, shadows act as central players in the drama of Western culture. Yet because they work silently, artistic shadows...