I found several other patents today that reference to the (indeed) french Kalle patent, but I am still not sure what the original patent says about gum. Anyway for me and Rob it doesn't work apparently. I also tested DAS with casein, and indeed it works. I'll post my findings with the synthetic collo´ds (PVA, PVP) soon. At this moment I find exposure times in the range of 15 seconds (!) with one collo´d/DAS mix. Tonal scale is rather short. Synthetic colloids come in various grades, each with their own specifications. Molecule length, degree of hydrolization etc. That makes it difficult to understand all variables. I have been looking through piles of patents with references to aromatic azides, DAS and collo´ds. Very interesting. Kosars' book is still a great standard though.
Originally Posted by CMB