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 07:25:23 2004