Hidden behind the displays of many museums live the conservators, a tribe dedicated to exploring the effects of dust, grease, light and air on some of the nation's most prized possessions. This is a world of science, art, history and innovation where the aim is to extend the life of objects so they can be appreciated by generations to come. But in a mutable world what should we keep and for how long? Narrated by Brian Gear. Producers Clare Hughes and Mary Price