U of S | Mailing List Archive | alt-photo-process-l | RE: I have a question

RE: I have a question

Ryuji,

Sorry, but I have to agree with Bob.  The alt-photo list is not a list
based on standards or hard science.  In an ideal world, all here would
be able to deal with the rhetoric and nomenclature of the science of
chemistry in the service of photography.  It's my sense that
traditionally this list has been a notch or 2 down the ladder; more
art than science.  If you've gleaned some insights from your readings,
and from your ability to interpret what they mean, we would all be
better served by a more direct interpretation rather than a simple
refernce to the literature.

--greg


On Sat, 20 Oct 2007, BOB KISS wrote:


DEAR RYUJI,
	Please help here.  I try to follow the rule of my last name,
KISS, which stands for "Keep it simple stupid".  I can't deal with hundreds
of examples.  You are the chemistry man so please suggest just one or two
excellent silver bleach alternatives to potassium ferricyanide that would
work and be more environmentally friendly (as well as regulation free),
given standard silver gelatin processing procedures...yes, thiosulfate fix,
washing, etc.  It would be nice if they were readily available chemicals.
To keep it simple, let's assume that we would want to bleach prints before
toning.
	What do your recommend...
			CHEERS!
				BOB


-----Original Message-----
From: Ryuji Suzuki [mailto:rs@silvergrain.org]
Sent: Saturday, October 20, 2007 6:49 PM
To: alt-photo-process-l@usask.ca
Subject: Re: I have a question

From: Richard Knoppow <dickburk@ix.netcom.com>
Subject: Re: I have a question
Date: Sat, 20 Oct 2007 14:29:07 -0700


    Please give an example.

You can get hundreds of examples by looking up US Patent
5391466. Iron (III) complex of some of the the compounds
derived from Formula (II) in this patent, used alone, in a
weakly acidic buffer, are an excellent b&w bleach with
superior biodegradability. As usual of Konica patents it
includes a ridiculously long list of many compounds taht can
be potentially used, but one just has to think about which
ones are easy, fast and cheap to make and the list immediately
becomes much shorter. Fujifilm and AGFA also came up with
different compounds that may be used similarly. Perhaps the
compound (I) disclosed in US Patent 5149618 (assigned to AGFA)
is related to the former patent's Formula II, although this
compound is, of course, excluded from it. The best compound in
the Konica patent is more biodegradable than the AGFA one.

Bleaching agents that are one generation older, such as iron
(III) EDTA or iron(III) DTPA bleach is poorly biodegradable
but these are still much more preferrable to ferricyanide in
terms of environmental damage.

These compounds are also usable in mixture with thiosulfate as
a stable print reducer, but generally speaking, you can get
stronger bleaching action when bleach is used alone (oxidation
potential is 100-200mV higher without fixer mixed in).
--
Ryuji Suzuki
http://silvergrain.org

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