Re: Dark reaction
Dichromated colloids, particularly after being coated and dried, begin to insolubilize (harden) -- even if not exposed to light (hence, "dark reaction" -- not *caused* by darkness, but happens even in darkness). This tends to fog dichromated-colloid media rather quickly. It is more rapid at higher temperatures, and there is some evidence it is more rapid at higher ambient humidity.
Here is a link to a scholarly article from the electronics screen printing industry, which discusses the dark reaction beginning at p. 2 ("Light appears to accelerate an insolubilization which occurs slowly in the dark (dark reaction)."). [NOTE: if the URL gets broken going through the list server, you may have to reassemble it]:
The article also discusses sensitivity as a function of dichromate concentration.
Kosar's book, "Light Sensitive Systems," which is cited in the paper, is an excellent source of information on these topics.