From: Richard Knoppow (dickburk@ix.netcom.com)
Date: 02/17/03-03:24:01 PM Z
----- 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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