From: Philippe Monnoyer (philippe.monnoyer@skynet.be)
Date: 02/17/03-05:36:32 PM Z
Hi Richard,
Well, a rehalogenating bleach won't work at all for reversal. These bleaches
contain either bromides, chlorides or iodides.
In the reversal process, the purpose of the bleach is to remove the black
silver image WITHOUT replacing it by silver halides (rehalogenating bleach).
If you do so, you transform the image back to what it was before
developpment, namely silver halides. So, you end up with an homogeneous
film/paper, like unexposed. If afterwards you developp it, everything will
turn black.
An adapted single bleach would have removed the first silver image, leaving
nothing else in the film/paper. That way, the second developpment will make
all but the initial image turn black. That's the reversal process.
I think copper sulfate with a touch of sulfuric acid, like for dichromate
bleach, or permangante bleach will work OK. Try different concentrations.
Rinse thouroughly to eliminate silver sulfate.
And keep us aware of the result,
Cheers,
Philippe
----- Original Message -----
From: "Richard Knoppow" <dickburk@ix.netcom.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Monday, February 17, 2003 10:24 PM
Subject: Re: Bleaches
>
> ----- Original Message -----
> From: "Jack Fulton" <jefulton1@attbi.com>
> To: <alt-photo-process-l@sask.usask.ca>
> Sent: Monday, February 17, 2003 12:00 PM
> Subject: Bleaches
>
>
> > Thanks Philippe:
> > I am using the bleaches for reversal only. A
> rehalogenating bleach, such
> > as that for a sepia toner might work . . what do you
> think?
> > Best
> > Jack
> >
> > > Yes, for example bleaches based and ferric salts or
> cupric salts. I don't have
> > > my litterature right now, but let's say that an acidic
> copper sulfate would
> > > work, I guess. Or ferric EDTA would be good as well.
> Sorry I don't have exact
> > > formulations at hand now.
> > >
> > > Philippe
> > >
> > > PS: Jack, are you using rehalogenating bleaches or is it
> for reversal only ?
> > >
> > > |On 14.02.03 Monnoyer Philippe wrote:
> > > |(but this is a different thread!)
> > > |>I personnaly would tend to use non-toxic bleaches
> based on
> > > |other formulations.
> > > |
> > > |May you be more explicit?
> > > |
> > > |
> > > |Alberto
> > > |
> > > |
> >
> In normal reversal processing the bleach is of the type
> which dissolves the metallic silver rather than converting
> to a halogen as in indirect toning. The traditional bleach
> is dichromate and sulfuric acid. Because of the hazards of
> dichromate an alternative potassium permanganate bleach has
> been suggested. I am not so sure it is any less hazardous
> than dichromate plus dichromate is used in many alternative
> processes. There may be newer bleaches which accomplish the
> same purpose.
> The idea of reversal is that after first development the
> undeveloped silver halide is in the form of a positive
> image. If the negative metallic silver image is removed, the
> remaining halide can be fogged and developed into a positive
> silver image.
> One can also treat the film with sulfide after the first
> development. This creates a positive silver sulfide image.
> The metallic silver image can then be removed using
> essentially Farmer's reducer, which does not affect the
> silver sulfide. The only drawback to this is that the
> resulting image is sepia. Sulfide can also be used for
> redevelopment in conventional reversal, in which case it
> needs no fogging exposure.
> In color processing the final image is composed of dyes so
> Farmer's or a variation of it can be used for bleaching. One
> can not use color blix for B&W reversal, however, since it
> removes both silver halide and metallic silver. Probably it
> could be used after a second development using sulfide with
> no intermediate bleaching.
> ---
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@ix.netcom.com
>
>
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