A boat tilts on a huge wave, sailors fight the ropes, and Christ sleeps at the stern. Rembrandt painted only one seascape, in 1633, and in 1990 it was cut from its frame and stolen. It has never been found.

In Correggio's Holy Night there is no lamp, no moon and no fire. The light comes from the newborn Child, and it is so strong that a shepherd girl shields her eyes. Here is how one Christmas painting taught Europe to paint the dark.

Before electricity, painters had one instrument for drama: the way light fell across a face. A short tour of how the old masters used shadow.