[pure-silver] Re: Pyro in a Jobo Processor
- From: Ryuji Suzuki <rs@xxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Mon, 21 Mar 2005 13:00:06 -0500 (EST)
From: "John Black" <jblack@xxxxxxxxx>
Subject: [pure-silver] Re: Pyro in a Jobo Processor
Date: Mon, 21 Mar 2005 12:04:00 -0500
> Can't think why Ca and/or Mg sequestration might improve DNA
> mobility in gel... this might have implications for photography as
> the gelatin layer is a gel also and silver halide/sliver granules
> may have some degree of mobility (undesirable, as it might lead to
> graininess) but no electric field is applied to the film (not on
> purpose that is).
As far as I know there is no solid report relating grain mobility to
graininess. Developing grains move slightly when filament is forming
rapidly, but this is only visible under electron microscope. Silver
halide crystals are usually 0.1 to 1 micron in diameter and the net
volume is reduced when developed because halides are released into the
developer leaving denser silver. Gelatin has strong adsorption on
silver halides and that is probably enough to prevent grains from
dislocating in gelled gelatin. In modern commercial emulsions,
silver-to-gelatin ratio is probably 1 or higher in mass, but in terms
of volume in dry layer, it's about 0.05 and in swollen gelatin layer
even smaller. These ratios are smaller in older commercial emulsions
which generally had more gelatin per silver coating weight.
Different degrees of graininess of developer solutions can be
explained by the factors affecting the morphology of developed grains,
and so far no one has established "mobility" of silver has anything to
do with graininess or morphology of developed silver.
Also, I think electrophoresis is done on crosslinked polyacrylamide or
maybe some other polymer, which is quite different from gelatin.
--
Ryuji Suzuki
"Keep a good head and always carry a light camera."
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