Re: Image formation in gum

On Dec 18, 2005, at 7:53 AM, Katharine Thayer wrote:

>
> As I've said many times throughout this discussion, when you've got
> excess pigment, you're going to get pigment left on the substrate
> whether or not the gum is exposed, as I demonstrated by cutting the
> coated paper in half and exposing half and not exposing half and
> finding that I had the same pigment tone on both halves of the paper
> after development, as long as I used a hyper-pigmented emulsion. I
> did the same thing with the glass, as I described, confirming that
> both on glass and on paper, the excess pigment thing is an
> extra-photographic phenomenon. It's a function of pigment, pigment
> concentration, sizing and paper, and not a function of exposure.

Clarification: Here I was thinking only of the specific case of excess
pigment on paper rather excess pigment in general. The point is that
the excess pigment thing, as far as I have been able to determine, is
a function of some (not well understood) interaction between the
particular pigment, the concentration of that pigment, and the
substrate and its preparation, and is a phenomenon that occurs
alongside, rather than within (hence the term extra-photographic) the
photographic process. I suppose you could say that under some
conditions, those that produce the tonal inversion thing, exposure is
involved in a negative way, in that the excess pigment is deposited
only where exposure doesn't happen, but that's different from saying
that exposure is involved in creating the deposit of pigment stain; I
think my experiments show pretty clearly that it's not.
Katharine
Received on Sun Dec 18 10:43:07 2005