[pure-silver] Re: Chemical Fogging in Reversal Processing
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Fri, 18 Aug 2006 13:56:29 -0700
----- Original Message -----
From: "Jordan Wosnick" <jwosnick@xxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, August 18, 2006 9:04 AM
Subject: [pure-silver] Re: Chemical Fogging in Reversal
Processing
John Banister wrote:
After first development and bleaching, then I can chose
to either fog the film and redevelop
or to proceed directly to sulfide or selenium toning, and
these operations can be done in the
same manner for all films because they are carried out to
completion. Is this approximately
correct?
Hi John,
It is correct for sulfide/thiourea, but not for selenium,
as far as I know. I'm not sure what reaction, if any,
occurs between selenium toner and silver halide. In any
case, commercial selenium toners like KRST contain
fixer-like ingredients which will degrade your positive
silver halide image as you try to "tone" it.
If you use light-fogging followed by re-development, you
can selenium-tone your film after fixing to "deepen" the
image tone. I've read speculation that a toning step like
this is part of the Scala process.
Jordan
--
Jordan Wosnick
jwosnick@xxxxxxxxxxx
Kodak Rapid Selenium Toner will tone silver halide, and
in fact, was, in the past, recommended by Kodak as an
alternative to the Sodium Sulfide test for completeness of
fixing. I am not sure how much effect on density the fixer
in it results in. The solution is mostly Ammonium
thiosulfate so its likely to have some bleaching effect.
Sulfide is a standard alternative to regular developers for
reversal processing.
The color produced by any toner is, to a large extent,
dependent on the nature of the Silver. In the case of
indirect toners, that is toners which employ a bleach step
before toning, the image color after toning depends on the
nature of the bleach. Many years ago Defender published a
set of formulas for indirect toner for Varigam paper. These
toners used Thiourea (AKA Thiocarbamide) as the redeveloper.
There were three bleaches and three Thiourea variations. The
combination of one bleach and one redeveloper allowed a
range of image color.
In the case of reversing film the halide being
redeveloped is the original halide so changing the bleach
will probably not have an effect. Bleaching in reversal is
different from bleaching in indirect toning. The reversal
bleach removes the metallic silver completely leaving
undeveloped halide behind. In toning the silver image is
converted back to a halide. By varying the bleach one can
choose the nature of the Halide.
For Thiocarbamide redevelopment its possible that
adjustment of the pH may have an effect on the final image
color. If I interpret the Varigam formulas right increasing
pH should result in colder tones. I will copy this below.
As a rule, in print toning, the finer grained the
original image the yellower the toned image will be. So, I
suspect the very fine grain of T-Max may be responsible for
the unpleasant yellow color. When used on paper indirect
toners are supposed to be best for cold and neutral tone
papers and to result in a excessively yellow color when used
on warm tone papers. While film grain is generaly quite
large compared to paper grain its possible the same sort of
thing is happening.
Varigam Toner T-1
Water 500.0 ml
Thiocarbamide 3.0 grams
Sodium Hydroxide 6.0 grams
Water to make 1.0 liter
As always be very careful when dissolving the Hydroxide
because it evolves great heat and can boil and spatter. Use
heat proof containers for mixing.
Another possible redeveloper is Kodak Brown Toner. This is a
direct toner consisting of "Liver of Sulfur". While it works
on silver without a bleach it will also work directly on
halide. KBT on paper results in a colder Sepia than indirect
toners.
As pointed out in the previous post a reversal image of
silver can be toned in any conventional toner. KBT will also
slightly intensify the image. When used for protecting
microfilm it results in a _cooling_ of the image color
rather than a brown or sepia color, it _may_ have a similiar
effect on reversed T-Max. This is due to the nature of the
silver. Ryuji Suzuki can probably explain the mechanism in
detail.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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