Re: Modifying bleaches

From: MARTINM ^lt;>
Date: 11/29/04-06:18:50 AM Z
Message-id: <005301c4d60d$afe7cee0$550edb50@MUMBOSATO>

"The bleaching agent seems to need to be potassium ferricyanide, or maybe
Potassium permanganate, or a dichromate."

Actually, there are a great many oxidizers that can do the job - from copper
sulfate to ceric sulfate (not to mention nasties like bromine and the like).

"Unless I am told I really need something else, just from a safety
standpoint, ferricyanide looks like my choice."

Ferricyanide can be replaced by Fe-EDTA or ferric sulfate, which do less
harm to the environment.

EDTA (2Na) 30g
Fe(III) Sulfate 30g
Potassium Bromide 30g
Sodium Hydrogen Sulfate Crystals 30g
Water to 1000ml

Note, this formula applies to ultra-fine grain (Lippmann) emulsions. For
coarser grains you might have to increase the concentration of the bleaching



----- Original Message -----
From: "Charlie Goodwin" <>
To: "AltPhoto List" <>
Sent: Monday, November 29, 2004 6:38 AM
Subject: Modifying bleaches

> I have become interested in the, new to me, subject of rehalogenating
bleaches, both for the flexibility they appear to offer for toning, and for
the potential to "turn" a paper of whatever flavor, bromide, chlorobromide
or chloride, into a bromide paper or to a chloride paper, or an iodide paper
etc.and to redevelop it as such, and also to be able start with a paper as
whatever it is, and then to tone it as whatever else I might want it to be.
Seems awfully adaptable.
> I have no knowledge of the chemistry of bleaches, and wish to proceed
safely. I am hoping more knowledgeable persons could tell me that either
my guesses are correct, or if I am off base, to tell me what I need to know.
> From browsing the web and scanning through "The Darkroom Cookbook" it
appears that the keys to rehalogenating bleaches are a bleaching agent and a
source of a halogen, chlorine, bromine or iodine.
> The bleaching agent seems to need to be potassium ferricyanide, or maybe
Potassium permanganate, or a dichromate. Unless I am told I really need
something else, just from a safety standpoint, ferricyanide looks like my
> And then a halide source, potassium bromide, potassium iodide or sodium
> I found in "The Darkroom Cookbook" a bleach called a rehalogenating Bleach
and several very similar looking bleaches like the DuPont 6-T Toning System,
which deploys three different bleach baths for varied effects:
> Varigam Toning Bleach 6B-1
> Potassium Ferricyanide 22g
> Potassium Bromide 25g
> Water to make 1000ml
> Varigam Toning Bleach 6B-2
> Potassium Ferricyanide 22g
> Potassium Iodide 10g
> Water to make 1000ml
> Varigam Toning Bleach 6B-3
> Potassium Ferricyanide 22g
> Sodium Chloride 35g
> Nitric acid 15ml
> Water to make 1000ml
> These are ordinarily followed by toning baths.
> I presume these Varigam Toning Bleaches are all rehalogenation bleaches
which could be used to reduce a print back to a silver halide and followed
by a simple redevelopment in one or another common developer.
> My initial question is that I wonder if chloride rehalogenating bleaches
like Varigam Toning Bleach 6B-3 could be modified by using hydrochloric acid
rather than nitric acid.
> That quickly becomes several related questions. Would it be safe to do
so? Would it work well? I am hoping to use, wherever practicable, common
household chemicals or commonly available items like muriatic acid. If I
can get along well without ever needing nitric or sulfuric acids and super
concentrated acids I would be glad. But, if I do need to use nitric or
sulfuric acids, can they and should they be obtained in lower
concentrations? Would that create other issues? Cost is less an issue
than safe handling.
> Reading about ferricyanide bleaches, the precautions I see say that
ferricyanide is generally not a dangerous source of cyanide gas unless it is
mixed with strong acids. I am guessing that the 15ml of nitric isn't
enough to create that hazard. I hope I can use hydrochloric in a similarly
safe manner (or safer). I don't want to mess around with safety on this
> Thanks in advance!
> C
Received on Mon Nov 29 06:20:41 2004

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