How did Francis Bacon's painting materials differ from those used by Hogarth? How did Whistler achieve harmony in his paintings and what was the legacy for his pupils and followers? How many different yellow pigments did Gainsborough use to mix the colour of John Chafy's cello and what is their effect? These and other questions can now be answered by the advances in scientific analysis that have shed new light on the working practices of artists of all periods. Revealed here in thirty intriguing case histories are results of the study of British paintings at the Tate Gallery. These investigations, described by the conservators and scientists who worked together to examine each painting, are recorded in non-technical language for everyone interested in the creative process and its impact on our understanding of art.