[pure-silver] Re: Development modifications for higher sharpness

From: DarkroomMagic <info@xxxxxxxxxxxxxxxx>
Subject: [pure-silver] Re: Development modifications for higher sharpness
Date: Tue, 26 Apr 2005 18:11:24 +0200

> Do you think it's different films or different grain sizes? In other words,
> will fine grain react differently to large grain, or is it just a different
> reaction depending on emulsions regardless of grain size?

You can't separate those issues because if you change the grain size
then you've made a different emulsion.

Most film emulsions are made of multiple layer
structures. Conventional emulsions are typically octahedral shape and
more modern ones are tabular grains of various types (usually thin,
high aspect ratio). In both types, the core part has very high iodide
content (10 to 40% iodide, rest bromide) while the iodide content is
kept low near the surface. If you find an optimal profile for very
fine grain emulsion, and then scale the profile by a constant factor
to make a large grain emulsion, the profile is quite off the optimal
distribution for that size.

I generally recommend DS-10 for conventional films and 400-speed
tabular grain films, and DS-12 for slow tabular grain films. I've also
used DS-10 at 1+2 dilution for Acros 100, T-MAX 100 and APX25 with
very good results. In sensitivity to different developer compositions,
I think 400-speed conventional emulsions are generally more responsive
to different developers than 100-speed films or tabular grain films.
These are the films that contain most silver in each square meter and
produce most reaction products during development.  However, I've seen
some tabular grain films changing apparent grain to developers
containing diethanolamine-sulfur dioxide adduct. Emulsion makers can
use various other techniques other than tabular grain crystals in
order to save silver, expedite development, increase speed,
etc. Polymers blended to gelatin can have quite a bit of influence on
the photographic properties of the emulsion as well, and some can
change the way the emulsion reacts with the developer.

Any of these can influence on the sensitivity to a change in developer
composition.

--
Ryuji Suzuki
"Keep a good head and always carry a light camera."
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