A single harsh beam of light hitting half a face in a pitch-black room triggers instant drama, and artists have exploited that hardwired reaction for more than two thousand years. This episode traces chiaroscuro, the Italian term for light-dark, from the lost shadow painting of the Athenian Apollodorus and the stag hunt mosaics of Pella to its status as one of the four canonical painting modes of the High Renaissance, alongside sfumato, cangiante, and unione.

We look at Queen Elizabeth I demanding shadowless portraits painted outdoors, the multi-block chiaroscuro woodcut and the forged dates of Lucas Cranach the Elder, the German key-block style versus the softer Italian approach, and St. Bridget of Sweden's vision of a glowing infant that gave Northern painters a new light source. From there the story darkens into Baroque tenebrism with Ca ...