[pure-silver] Re: Speed rating of glass plates
----- 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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