[pure-silver] Re: Speed rating of glass plates
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Fri, 29 May 2009 21:16:59 -0700
----- Original Message -----
From: "Bogdan Karasek" <bkarasek@xxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, May 29, 2009 7:38 PM
Subject: [pure-silver] Re: Speed rating of glass plates
Hello Richard,
Thanks for responding. I have a several old "British
Journal Almanac" so that would be a good start. In
several of the unopend plate boxes, there were sheets of
paper with formulas for film developpment, times. I'll
have to have a closer look. Still, I wonder if any of
the glass plates had the modern equivalent of at least 50
iso. I've some group portraits where you can see that
somebody moved their head, or hand.... two ghost images,
so exposure times must have been quite long. No wonder
they had those chairs with the neck brace to keep the head
steady as the person dozed of during exposure :) No
wonder all these portraits are so stiff looking.
They make beautiful contact prints. And a 5x7 plate was
a perfect size; good proportions. 8x10 seems a bit off
for portrait work, especially with the long side of the
back in the vertical position. And not as heavy.
Thanks,
Bogdan
I figured out from some old Kodak, or maybe it was
Dupont, that "Par Speed" film was about ISO-20. I suspect
many of the really old emulsions were around ISO-5 to 10,
especially those made before the discovery of gold
sensitizing.
It would be interesting to see some of the old
formulae. The ones I have seem to be more alchemy than
chemistry.
If these films have latent images on them a great deal
of care is needed. Anti-fog agents will tend to destroy
whatever is there. I am not sure what magic is used in
recovering the images from really old film but I think one
method is to use very high contrast, nearly lith type,
developers at very low temperatures. I do not know the
theory of this. If these plates have been subjected to much
moisture or high temperatures there may not be anything on
them by fog.
There is a fellow who specializes in recovering old
images. I am off to work in a few minutes so I don't have
time to look right now but will tomorrow.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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