Sarah Greenough, senior curator of photographs, National Gallery of Art, and Roger Taylor, professor of photographic history at De Montfort University, Leicester. Two methods of fixing an image dominated the early days of photography: the one-of-a-kind daguerreotype and the replicable calotype, which was made using paper negatives. In the second of this two-part episode, Gallery curator Sarah Greenough and Professor Roger Taylor of De Montfort University discuss some of the best calotypists, the subjects that fascinated them, and the slow death of the medium as it was supplanted by more popular photographic processes. Produced in conjunction with the exhibition Impressed by Light: British Photographs from Paper Negatives, 1840-1860.