Re: tricolor gums
Another debt I owe Greg Schmitz is that he introduced me to the 21-step sensitivity guide, which turned out (for me at least) to be the Rosetta Stone of gum printing. (Almost) anything I really need to know, I ask, & it tells. Which is why the present talk about timing for color seps seems dubious. I mean, how can you tell "exposure time" (either "standard" or ad hoc) for any color without mentioning development as part of the equation?
I haven't tested this recently (since I develop by eye, not time), but as I recall, the "curve" of a gum mix changes with development. If, say, you increase exposure AND development, you get a different "curve." Also, if
you lower the depth of pigment, the scale gets longer, and vice versa. Etc. Each person's "standard exposure" is therefore geared to their strength of color, dichromate, AND development... (for starters).
Even if someone else uses the same "mix," their water, paper, humidity, mind waves, method of coating, pollution level, and myriad other variables, will still vary.