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Re: Garet's question about gum exposures



On Thu, 9 Mar 2000, Sarah Van Keuren wrote:
> 
> I have noticed the same phenomenon and have learned to compensate for it by
> adding 10-15% exposure time with each layer just to penetrate to the same
> place as the previous exposure in the highlights. My theory is that each
> layer of gum bichromate emulsion lodges in the tooth of the paper and
> smoothes it. Longer and longer exposure times are needed to bind the
> emulsion to the increasingly slippery print surface. 

But the gum emulsion remains LEAST in the highlights, if at all, and
Garet's finding is the opposite... rather you both find shadows build up
more. I was puzzling over this (not a finding I've found, incidentally)
and was tempted to say because dichromate has a tanning effect so the
paper is tanned -- but that still wouldn't explain why there would be more
tanning in highlights... And I've also found that the shadows can build up
so much density a new layer is hard to even apply -- it crawls (a drop of
Tween 20 is a godsend). But then Sarah described resizing....

>After three layers I
> resize with a layer of gelatin that I harden in dilute formaldehyde and this
> seems to restore some tooth to the paper as well as preventing pigment from
> attaching to highlights where the original sizing may be worn down by
> abrasion. There is not such a problem in the heavily printed parts because
> the layers of emulsion function like a slick, non-toothy sizing.
 
If the resizing restores ability to hold highlights as you say, that might
mean that the dichromate has tanned the *gelatin* & resizing renews it.
But I'm wondering why I didn't notice that, maybe because I generally use
flat negs where highlights print fully ? Sometimes (not always) I change
formula for subsequent coats -- making emulsion thinner (adding water) and
color weaker... Or, something. (In this Stieglitz was right -- every gum
printer has a different process...)

Judy


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| Judy Seigel, Editor                           >
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