Re: Dry Plate Speed & Shelflife

From: Robert Newcomb <newcombr@uga.edu>
Subject: Dry Plate Speed & Shelflife
Date: Tue, 01 Mar 2005 11:53:28 -0500

> 1) I have read that the speed of early dry-plates was about 7 stops
> slower then the wet -plate process in use at the time. While I'm
> certainly not trying to shoot action sports shots, we're talking Very
> slow here. I have heard that the bottled silver emulsions have an in
> camera speed of about ISO 1/2- maybe 1.

It all depends on how your emulsion was prepared. I assume you have
one of the commercially available liquid emulsion product. Those
comments about silver gelatin process from early 1870s apply to those
1870 stuff and not today's emulsions. Maddox published his emulsion as
a positive slide emulsion to be used by contact printing, and he did
not make it as a camera negative emulsion. It was the BJ editors who
encouraged readers to pursue this technology for negative use. Speed
of silver gelatin process was improved since then, so when you are
comparing speeds, you need to pay attention to which emulsion you are
talking about.

Also, I suppose the bottle you have was made and sold for printing,
not for camera negatives. Printing emulsions are of course slower
speed and higher contrast and that is a wrong material to use in
camera if you are after the best result.

> 2) I have also understood that early dry plates (hand poured) had a
> useful shelf-life of only a few days or a week after being made in
> which one must expose them. Is their a means of extending this
> shelf-life to a couple of weeks or at least something more the a few
> days? I'd hate to make them and then not be able to go out shooting
> the next day so the plate spoil.
> I understand that commercially prepared plates later overcame these
> factors but what is possible of the home brewer?

Early emulsions were made with excess silver and the emulsion was not
desalted. Since these issues baceme known, decent bromide emulsions
are prepared with excess halide and the emulsions are desalted before
digestion. Also a whole book's worth of organic and inorganic emulsion
stabilizing compounds are known and emulsion's stability has been
greatly improved, and what you said probably don't apply to the
commercial product you have.

--
Ryuji Suzuki
"Well, believing is all right, just don't let the wrong people know
what it's all about." (Bob Dylan, Need a Woman, 1982)