From: Richard Knoppow (dickburk@ix.netcom.com)
Date: 06/30/00-03:53:04 PM Z
At 10:52 PM 06/28/2000 -0400, Sarah Van Keuren wrote:
>In a most incredible example of synchronicity, as I hit the send/receive
>command to send the message that you responded to below, Andre, I received a
>message from Steve Puglia who'd done the research at the Library of
>Congress. I hadn't heard from him in ten years. I sent him what I'd written
>and he replied with the following helpful clarification:
>
><Your recollection about the polysulfide toning providing a greater degree
>of
>protection is correct. Here is the scoop- feel free to pass on this
>information:
>
>Much of the research investigating the effectiveness of various treatments
>to
>protect photographic materials from silver image deterioration was conducted
>by
>the Image Permanence Institute (IPI) in Rochester, NY, in conjunction with
>work
>that was being conducted in a standards subcommittee of which I was chairman
>at
>the time (the standards organization is the Photographic and Imaging
>Manufacturers Association, PIMA).
>
>There are two approaches to protecting image silver, first is to convert the
>silver to a more stable compound and second is to provide a protective
>barrier
>around the metallic silver. This will work for both black-and-white
>silver-gelatin films and papers.
>
>The conversion approach is done basically by toning, although that term is
>somewhat of a misnomer because toning implies an intentional change of the
>image color (which is not usually desired with most images on film and may
>or
>may not be desired with prints). The standards group prefers to refer to
>the
>conversion approach as a protective treatment, rather than toning. The
>degree
>of protection is directly proportional to the degree of conversion. The IPI
>research showed selenium and gold treatment was usually only a partial
>conversion, while conversion with the polysulfide treatment was much more
>complete. Also, the silver sulfide that is formed with polysulfide
>treatment
>is very stable and unreactive to almost all types of pollutants or
>contaminants. Kodak Brown Toner can be used for this type of treatment.
>
>The second approach, providing a protective barrier, does offer a degree of
>protection, but like the gold or selenium treatment it does not offer as
>much
>protection as the polysulfide treatment. Agfa and Fuji both sell products
>for
>this type of treatment, Agfa Sistan and Fuji Ag-Guard. The Agfa Sistan has
>been sold in the USA and may still be available, but I have not seen it in
>stores in years and it would probably have to be ordered. I do not believe
>the
>Fuji Ag-Guard is available in the USA. Based on their testing, these
>manufacturers feel these products offer reasonable protection for silver
>images
>and that the full conversion approach is not necessary in the real world.
>
>
>>>... a fellow grad student in
>>>photography at the University of Delaware, later working at the Library of
>>>Congress, found that pure selenium did not protect silver as claimed.
>>>Selenium-toned microfiche was getting just as much foxing as untoned.
>>>
>>>Hidemi Yokoto, then a grad student in photography at Tyler School of Art,
>>>translated Steve's article for Japanese photographers. Word had not reached
>>>Japan at that point (about 10 years ago) and Kodak was promoting selenium
>>>toning for archival permanence over there which seemed a pity with the
>>>existing mercury contamination, etc.
>>
>> With due respect, Sarah, but thats at best half-true. The one half
>> is this: Most people (including myself) use selenium at a dilution
>> and for a time that lead only to a replacement of silver on the
>> surface of the grain. That is quite enough for imparting the kind of
>> colour change that one expects from selenium toners. The other half
>> is that selenium is a much more stable metal than silver. Thus, if
>> you tone with selenium you will always have _some_ archival
>> advantage. If you tone with a strong solution for a sufficient time
>> you will get a print as archivally permanent as you can reasonably
>> wish for.
>>
>> Andre
>>
>>
FWIW, the IPI research is reported in a paper available over the web.
See the Conservation On Line site at: http://palimpsest.stanford.edu The
paper is:
"Stability of black-and-White Photographic Images, wiht Special Reference
to Microfilm" Reilly, Nishimura, Cupriks, Adelstein, _The Abbey Newsletter_
Volume 12, Number 5 July 1988
The complete research report is available from IPI for about $50.
To summarise, they found that microfilm treated with diluted Kodak Rapid
Selenium Toner showed redox spots and other signs of oxidation. In their
experiments they found that the work of Drago, Wood, and Lee, on which the
Selenium toning recommendations were based was flawed. It turns out that
the toner used in the research evidently contained an impurity which
resulted in sulfiding of the iamge. It was the sulfiding, not the Selenium
which enhanced the permanence. They also found that Kodak GP-2, Gold and
thiocarbamide toner, a standard treatment for microfilm worked as well with
the gold left out also due to incidental sulfiding. Production Kodak Rapid
Selenium Toner does not have whatever caused the sulfiding.
In a personal communication with Dr. Nishimura he said that the problem
with diluted KRST was that it split toned, that is, it tones preferentially
the finer grains of silver, which tend to be most plentiful in the denser
partrs of the image, so that the dense areas may be protected but the less
dense areas are not. Silver selenide is as stable as silver sulfide but,
in order to get full protection of a silver image KRST should be used in a
dilution of not more than 1:9 and for at least 3 minutes at 68F.
The IPI "Silver Lock" formula is a modification of Kodak Brown Toner to
allow more predictable results as an image protectant. Nishimura recommends
the use of Kodak Brown Toner, a polysulfide toner, or ordinary pictorial
use, but has made no investigation into an optimum treatment.
Silver images which are _fully_ toned in a sulfide or selenium toner are
permanent, it is partial toning which is a problem.
Agfa Sistan is a solution of ammonium thiocyanate. This is one of the
substances used as a stabilzer in the stabilization process for
rapid-access printing. A very reliable source told me that it failed in
accelerated aging tests and, under some circumstances, may actually
accelerate the degradation of silver images.
In general, for silver or dye images, given reasonable processing the
storage conditions will have more to do with longivity than processing.
I will point out that "foxing" is caused by fungus and is not prevented
by any toning method.
Selenium is a transition element, not really a metal, and not a heavy
metal like mercury or lead, which are stored in body tissues. It does not
seem to be a particular envrionmental hazard although it is sometimes hard
to find out authoritative data about hazards.
---- Richard Knoppow Los Angeles,Ca. dickburk@ix.netcom.com
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