The largest of its kind in the world, the collection contains over 7,500 examples of historic black and white photographic paper.  Paul started the collection in the late 1990s to provide for scholars, researchers and collectors, an objective baseline for dating and authenticating photographic papers.  More broadly, the collection preserves the "genome" of black and white photography in its rich variation.  Acquired in 2015 by Yale University as a scholarly resource, the collection is the subject of active study and by the Lens Media Lab.  A spinoff application, the Backprinting website presents an index of manufacturer markings found on the reverse of photographs.