This is the first published monograph on the cyanotype process. It describes the history, chemistry, conservation, aesthetics and practice of photographic printing in Prussian blue. The unpublished experimental memoranda of Sir John Herschel, inventor if the process, are interpreted to unfold his discovery of iron-based photography, including his various formulae for cyanotype. The chemistry of the process is explained for the non-specialist, and many experimental variations on blueprinting are described. This book should interest photohistorians, curators and conservators of photographs, photoscientists concerned with 'non silver' processes and photographic print-makers who wish to use cyanotype today as an expressive artistic medium.