[pure-silver] Re: Sulfite stabilization
- From: Ryuji Suzuki <rs@xxxxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Thu, 05 May 2005 19:21:21 -0400 (EDT)
From: "John Black" <jblack@xxxxxxxxx>
Subject: [pure-silver] Sulfite stabilization
Date: Thu, 5 May 2005 16:12:22 -0400
> Some of you may remember that I am engaged in a developer component
> stability with time test using phenidone, ascorbic acid, tris buffer
> and sulfite. This study was undertaken out of sloth because I want
> to be able to make up film and paper developer and fixer out of
> stable liquids when I need them, not powders.
Incidentally, I've been pressing myself to come up with a way to
preserve ready-to-use developers or single stock developer
concentrates. I have been following the deterioration of DS-10 in
partially filled bottles without tight closure. The DS-10 as published
could be stored for 2 months or longer without any detectable change
in speed, contrast or other aspect of image quality. However, there
are some reports with gradual decline in contrast over time shorter
than 2 months. This is strange. At the same time, I've been trying a
few new stabilizing agents in place of, or in addition to,
triethanolamine and salicylic acid. Some of them seem to work
well. Details of this will be discussed when I have all information
ready, but this principle can be applied to a wide range of
developers. Some approaches use nontoxic chemicals but cost pennies
more. Others use agents of varying toxicity in a very small quantity
but they are cheap and effective. I haven't investigated whether new
agents would allow me to push the developer formulation to a zone
which is currently considered impractical, but there are
possibilities.
Also, I have Dimezone S from 3 different producers now, and I'm
comparing them as well. Visually, one made by the German plant of
James Robinson looks paler than the one made by the Indian plant of
Canton.
> I am up to 4 months now and see no loss of sulfite reactivity
> (reduction potential) from the saturated solution as compared with
> freshly made solution from powder.
In a tightly closed glass bottle, this is what's expected. The
question is when the solution is kept in partially filled bottles.
Kodak uses a mixture of sodium citrate and EDTA to slow down the
oxidation of sulfite in presence of air. They probably intervene
hydroxyl radicals, superoxides, transition metal catalysts, etc. This
is why Kodak HCA keeps better than plain 2% sodium sulfite bath.
--
Ryuji Suzuki
"Keep a good head and always carry a light camera."
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