Re: two questions about gum
(1) Charles, this makes sense; there's enough size in most watercolor paper as manufactured to keep the first layer from staining, but subsequent layers on unsized paper (depending on the paper) could well stain.
(2) I don't know that there's a rule of thumb for how to deal with this; people do whatever works for them, I suppose. If cutting the exposure time works, great. I can imagine that a drastic reduction in exposure might a similar effect to a reduction in pigment, but I've never tested that. I've just observed that many people who calibrate the emulsions individually find that when they print these emulsiions as layers in a tricolor, the tricolor ends up too dark. But it depends entirely on how people choose their pigment concentration in the first place, whether this is true or not. Since the pigment depth that people use for tricolor is entirely arbitrary and individually chosen, the depth chosen may be too much or too little; there's no way of telling until you print it as a tricolor. The fact that you've already established the best exposure for the mix while calibrating suggests to me that it's pigment and not exposure that's the problem. But as I said, whatever works, is the main thing.
I'm struggling with a similar issue, but finding that I have a different problem than many people have reported. After happily printing tricolor gum for decades by simply inverting the channels and printing greyscale separations, I've been experimenting with a more "sophisticated" approach, with less than satisfactory results. But the problem isn't that the print is too dark when the colors are layered over each other, it's that it's too light and too muddy, compared to the same image printed with the same emulsion by my old habitual method of simply inverting channels and printing,
But that's a subject for another post; I'll upload an examples and then maybe you can help me figure this out.
On Sep 25, 2007, at 3:43 PM, ryberg wrote: