Digital BW, The Print

> --- Anthony Atkielski <anthony@...> wrote:
>> What is silver extrusion?
>> 
> Silver extrusion is when due to poor processing, the
> silver in the paper begins to show through. It looks
> like the silver is sitting on top of the image. This
> is usually due to a lack of sufficient wash time with
> no hypo clearing agent used. It takes years to happen.
> It can be a challenge to minimize it with traditional
> copy methods. Not too tough with digital.
> 
> Evelyn

To be specific, the problem is called "silver sulfide staining".  They
appear on prints as a metallic sheen.  It is a very common problem and can
affect any silver photograph, even archival process, over time.  The problem
is commonly known as ordinary silver tarnish.   I have observed numerous
examples dating as recent as the 1970s.  The only known way to remove the
stain by copying is by cross polarized light.  This is accomplished with
filters on your light and your lens.  The polarizing sees right through it
with no problem.  Full instructions are on pg. 54-55 of Kodak's "Copying and
Duplicating" and this shows several examples.  I understand this can be done
with a digital camera, however I have never tried that.  I know that it is
not possible to modify a flatbed with polarized light as described above
because the scanner will fail it's calibration cycle.   For physical removal
of the staining from prints or negatives, see the extended tutorials in
"Fundamentals of Photograph Conservation: A Study Guide" by the National
Archives of Canada.  I have been doing these treatments for ten years now.
I can attest from experience that copying with cross polarized lights is so
effective that it is unnecessary to do any further treatment in the scan of
the resulting film copy, plus you pick up a full f stop of shadow detail.
This approach yields a much better digital file than any direct scan of the
deteriorated original.  This information applies only to prints,
deterioration of negatives is an entirely different treatment.
Thomas Robinson