[pure-silver] Re: Chemical Fogging in Reversal Processing
- From: John Banister <jbanister@xxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Sat, 19 Aug 2006 05:05:29 -0400
Thanks very much for the good information. I had thought that the
chemical similarity
between Selenium and Sulphur would allow for similar use, but now
I'll know to watch out
for this trouble with KRST. The toning and bleach solution formulas
for the Flemish Toner and
Dassonville T-56 toner at Jack's Photographic and Chemistry Site seem
pretty similar to the
thiourea carbonate sepia toner formula, though.
----- 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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