The gum-bichromate and Neblette's book

Robert Demachy prints

Mine

Two items for the aficionado of photography: An old photographic, non-silver, printing process text and a classic photography book. Except for the wealthy and knowledgeable, the old photographic processes [bromoil, carbon, cyanotype, ferro-gallic, gum-bichromate] are nearly extinct. They required great skill and patience...not characteristic of today's digital photography. Books on the old processes are scarce but a classic written by Robert Demachy who specialized in gum-bichromates is available online.

Photo-aquatint, or, The Gum-bichromate Process: A Practical Treatise on a New Process of Printing in Pigment Especially Suitable for Pictorial Workers by Robert Demachy

And a detailed general photography text by C. B. Neblette that covers the studio, cameras, darkroom, and motion picture.

1952 edition...

Photography Its Materials And Processes by C. B. Neblette

Robert Demachy [Wikipedia]

Gum-bichromate [Wikipedia]