From: Ryuji Suzuki (rs@silvergrain.org)
Date: 10/08/03-08:22:24 PM Z
I guess I don't need to get into chemistry because that topic is
pretty exhausted in pure-silver list. Here are a couple of trivia with
the way I see about history of developing agents.
The most common name to see in modern chemistry literature is
catechol. I don't see pyrocatechin or pyrocatechol often, except in
darkroom literature. (although, I think this is less confusing than
glycin without an e appearing in darkroom literature. It's like
calling guinea pigs as pigs.)
When discussing the alkalinity of developers, this article (as well as
many darkroom literatures) go by the buffering agent, but what matters
is the resulting pH. For example, one can easily make fine grain
developer containing sodium hydroxide. Ok, ok, that's obvious.
In that article somewhere, something like this was quoted: "developer
containing hydroxide is too alkaline and harsh for todays film" and so
forth. I've made emulsions, some from 1880's-like formula some more
modern variants, but I think plate developers of pH 11 range is pretty
harsh for old materials. (Terry has been developing his plates in a
catechol-hydroxide developer but he has had troubles with excessive
gelatin swelling.) Until I started thinking about making my own
emulsion I kinda believed with no reason old stuff gotta be tough, btu
it's not the case. The reason old plate developers had to have such a
high pH is of course because they lacked an efficient electron
transfer agent like phenidone or metol. Some had metol but still
buffered at 10 or above. Use of borates didn't really get recognized
until MQ-borax fine grain (D-76) of 1927 (which is 76 years ago) and
subsequent publications studying properties of MQ borax formulae. At
that time, electrical pH measurement system was not common among
photographic chemists (I didn't search for the year in which such a
device became available for lab use, but publications by people at
Kodak Research Laboratories from 1930 s don't have pH values
indicated, so I suppose they didn't have one. pH indicating reagents
were available but reading was coarse.). Anyway, the reason old
formulae used hydroxide or lots of carbonate should have in part to do
with necessity for high pH to get decent photographic speeds from
plates processed in pyrogallol solution, and also limitation of
chemical stocks, knowledge, tools and design techniques at that
time. After all, I personally find a developer similar to Microphen is
most suitable for classic plate emulsions, and that's what I use for
tray processing plates.
-- Ryuji Suzuki "Reality has always had too many heads." (Bob Dylan, Cold Irons Bound, 1997)
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