Re: Dark reaction
A couple of things: (1) The dark reaction is a particular kind of reaction that occurs with dichromated colloids coated into a film and should not be equated with "fogging." Fogging is any unintentional hardening of the gum layer. The dark reaction, if it proceeds quickly enough to result in fogging, can be included as a special case of fogging, but there can also be light fogging, which should not be confused with the dark reaction by using the same name for both. The dark reaction I've observed occurred in paper that was protected from light by being stored in a black envelope from photographic paper. http://www.pacifier.com/~kthayer/html/Darkreaction.html (2) I learned the hard way that fluorescent lights can fog a gum layer. When I moved into my present digs, with spacious workroom with fluorescent lights in the ceiling, I found that my gum was fogging, and I couldn't figure out why. I'd never had an opinion about fluorescent lights and gum before, so it didn't occur to me right away, but when no other reasonable explanation asserted itself, I tried turning the overhead lights off and coating under a lamp on the coating table with a tungsten bulb -- problem solved. Katharine |