Re: Confusing Speed and Sensitivity, (was Potassium vs. Ammonium Dichromate), (was Re: Clearing Gum Prints)

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From: Judy Seigel (jseigel@panix.com)
Date: 03/29/01-11:45:15 PM Z


On Thu, 29 Mar 2001, Sarah Van Keuren wrote:
> I haven't used potassium dichromate to speak of but have found pretty
> consistently using ammonium dichromate that 5-6 steps on a 21 step scale
> show separation with everything below the first step of separation dropping
> out and everything above the 5th or 6th adhering. I try to move that span of
> 5-6 steps up and down the 21-step scale, placing different colors in
> different places by varying exposure times through my continuous tone
> pinhole negatives. I imagine that with carbon prints all 21 steps would

Length of scale can be varied by increasing or decreasing pigment (more
pigment shorter scale), also longer soak (often, not always longer scale)
(I illustrate with step tablets for upcoming P-F -- should that happen to
occur one of these days..)

> In gum printing the top of the gum bichromate emulsion can harden like a
> layer of ice over a puddle but slough off entirely in the wash because it is
> not firmly attached to the support. I expect that you know what I'm talking
> about even if it seems cryptic to those who don't do gum printing.

Sarah, I wonder about that. I've always ASSUMED that the coat was simply
too thick, or too dark, that is that the light didn't reach down to the
part that was connected to the paper -- or is that what you're saying?
However, I THINK (tho haven't tested) that if you expose enough it will
hold... tho maybe no *steps* just 2 tones...??? (And would certainly
require contrasty neg so it didn't fog.)

Judy


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