Robert DEMACHY the Poitevin process to Georges Potonniée signed autograph letter

  

Signed handwritten letter addressed to the historian of photography Georges Potonniée, author of a History of the Discovery of Photography in 1925. He unofficially thanks Georges Potonniée: "If I have put in a lot of effort, I have only worked based on the data provided by the prolific Poitevin [the chemist and photographer Alphonse Poitevin], from which came the bichromated gum - collography on gelatin paper and its corollary the transfer." He will provide him, after some research, the desired details, however: "I fear that my knowledge may be quite limited.

" He concludes his letter with precautions to take in the future regarding frames: the potentially heavy risks are always the responsibility of the exhibitor.