What is it about scraps and fragments that make them so magical? Here, a piece torn from a 17th century manuscript gives us a glimpse of a portrait: one downcast eye, a broad nose, half a moustache. Nothing much - but the effect is like looking in one of those shards of glass in storybooks which act as portals to another world. Museums - and our own collections - are full of these portals. Where will they take you?