[pure-silver] Re: Pushing delta 400?
- From: Ryuji Suzuki <rs@xxxxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Wed, 02 Feb 2005 18:19:06 -0500 (EST)
From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
Subject: [pure-silver] Re: Pushing delta 400?
Date: Wed, 2 Feb 2005 14:10:20 -0800
> The main function of
> sulfite is to prevent oxidation of the developing agents. It
> accomplishes this through competing with them for oxygen.
> Development agents are all reducers, i.e., prolific
> absorbers of oxygen. This action of Sulfite tends to prevent
> the generation of developer reaction products. Since these
> are the cause of the border and edge effects which produce
> acutance, sulfite tends to suppress acutance. Another factor
> is the use of two superadditive developing agents, like
> Metol and Hydroquinone or Phenidone and Ascorbic acid. The
> combination of agents has a regenerating effect, each on the
> other. In other words less reacton products are generated so
> there is less acutance effect.
Richard, this is not quite. SUlfite is often involved in removal of
developer reaction products in the forms of quinone by sulfonation.
This has nothing to do with preservative action of sulfite, except
that sulfite is involved in both.
In metol only developers, sulfonation of oxidized metol is very slow
and some amount of sulfite should not markedly reduce accutance
effect. In phenidone-ascorbate developers, sulfonation does not
happen. Oxidized ascorbates are somewhat self decomposing in typical
developer conditions, and they do not interfare with the ongoing
development reactions, except possible local disturbance of pH.
--
Ryuji Suzuki
"Keep a good head and always carry a light camera."
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