Re: gum "stain" with zero exposure... etc.
Tom, I call it stain without the quotation marks, but in order to do that I broaden the definition of stain to mean a condition in which pigment is deposited where it's not wanted, not just a condition where pigment has soaked into an absorbent surface (usually paper) and left a permanent color change where it's not wanted. Maybe a different word would be better, but that one works for me. Like Tom, I've seen stain, as well as tonal inversion (which I consider a special case of stain) on glass, on yupo, and on other hard surfaces, as well as on well-sized paper. I agree with Tom that it's pigment all by itself, that it's hard to understand what's holding it to the glass surface since it can be easily brushed away, especially if it's lamp black, which is nothing but very fine filaments (soot, actually) it can be wiped off the glass with a fingertip or the edge of a tissue. It seems like it has to be some sort of electrostatic attraction, or something, but I don't know.
On Oct 7, 2009, at 4:27 PM, Tomas Sobota wrote:
Judy, far from me to claim that I understand what happens. I was commenting on your citing of Mike Ware: "The less viscous the emulsion...the more it soaks into the paper, hence the more stain". In the case of glass, where this tonal inversion or "stain" happens also, there's no "soaking into the paper" for any viscosity you might have, so the "stain" must have some other origin. According to what I have noticed, the pigment causing the "stain" just sits there on the paper or glass surface, apparently free of any gum. It is also very easy to remove manually (i.e. with a thin brush), since it doesn't seem to be bound to the surface in any obvious way.