Re: Modifying bleaches

"Could you tell me what these are, and what they do?
EDTA (2Na)
Fe(III) Sulfate
Sodium Hydrogen Sulfate Crystals
Are they all bleaching agents?"

No, ferric sulfate is the oxidizing part. Mixed with EDTA, it forms
Fe(III)EDTA. The sodium hydrogen sulfate is meant to acidify the solution.
Most photographic bleaches require an acid environment. In this particular
formula sodium hydrogen sulfate does replace sulfur acid (for safety
reasons).

"Also, since you mention your formula in relation to fine grain; I presume
that you are thinking about film."

Yes, very fine grain emulsions on film and glass plates.

  "I am, at least at first, concerned with print manipulation. Are there
different considerations for bleaching prints?"

I suspect (I have little experience with prints), grain size might play a
significant role.

"Are there similar formulations to yours that could convert silver back to
silver iodide, and/or to silver chloride?"

Though I never tried that, I believe you could replace the potassium bromide
by potassium iodide in the EDTA bleach I mentioned.

You probably know you can convert any silver chloride emulsion into a silver
bromide or silver iodide emulsion by simply bathing the silver chloride
emulsion in a potassium bromide or potassium iodide solution.
A silver bromide emulsion can be converted into a silver iodide solution by
using a potassium iodide solution.

In other words, it's possible to convert silver chloride into silver bromide
and
silver bromide into silver iodide. But you cannot do the opposite (convert
silver iodide into silver bromide/chloride or silver bromide into silver
chloride).

Martin

----- Original Message -----
From: "Charlie Goodwin" <cgoodwin@mcttelecom.com>
To: "AltPhoto List" <alt-photo-process-l@sask.usask.ca>
Sent: Monday, November 29, 2004 2:25 PM
Subject: Re: Modifying bleaches

> Hello MartinM,
>
> Thanks for an extremely prompt response! I'm afraid you are talking to
someone working at ignoramus level as far as chemistry knowledge goes. So
spelling it out kinda slow is in order. Or pointing me to references that
could walk me through if I am asking questions that require overlong answers
I am way behind the curve of knowing the basics of bleaching. I don't know
the nature and function of the compounds you mention, other than my
supposition that the potassium bromide is the source for bromine to change
the silver to silver bromide.
>
> Could you tell me what these are, and what they do?
> EDTA (2Na)
> Fe(III) Sulfate
> Sodium Hydrogen Sulfate Crystals
>
> Are they all bleaching agents?
>
> Also, since you mention your formula in relation to fine grain; I presume
that you are thinking about film. I am, at least at first, concerned with
print manipulation. Are there different considerations for bleaching
prints? Are there similar formulations to yours that could convert silver
back to silver iodide, and/or to silver chloride? I ask this since I am
looking, first, to get a set of tools to manipulate print tone through
redevelopment and/or toning.
>
> This is not to deny the utility to me of working on film. To get the
technical means to modify film images would be a bonus.
>
> Thanks!
>
> Charlie
>
>
> > "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.
> > E.g.:
> >
> > 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
> > solution.
> >
> > Martin
> >
> >
> > >
> >
> > ----- Original Message -----
> > From: "Charlie Goodwin" <cgoodwin@mcttelecom.com>
> > To: "AltPhoto List" <alt-photo-process-l@sask.usask.ca>
> > 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
> > choice.
> > >
> > > And then a halide source, potassium bromide, potassium iodide or
sodium
> > chloride
> > >
> > > 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
> > one.
> > >
> > > Thanks in advance!
> > >
> > > C
Received on Mon Nov 29 11:50:40 2004