When John Cyr set out to photograph the tools of the darkroom he discovered in himself something unexpected - a passion to capture the chemical fingerprints of some of the world's greatest photographers.

His book Developer Trays documents dozens of simple trays textured by each user's unique chemical process. Discoloured, scratched or pristine, each tray is an artefact of an artist at work.

Photographed with a museum catalogue level of precision and beauty, every image reflects Cyr's deep respect for the darkroom process - a process rapidly disappearing with the advance of digital photography and ink jet printing.

Produced for the BBC by Jennifer Hamblett and Lisa Rinehart

Picture This is a series of video features published every Thursday on the BBC News website which illustrate interviews with authors about their new books.