From: Sarah Van Keuren (svk@steuber.com)
Date: 06/28/00-08:52:46 PM Z
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
>
>
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