Copying old photos

I see that I may have to clear up some question about photocopying.

First of all, thank you Bob Kosovsky for the plug.

I don't specifically recall the question about copying old photographs
from last year, but it comes up fairly often.  The very old photographs
(salt prints, albumens, matte collodion, glossy collodion and gelatin
POPs) all are "developed" by light.  The term POP means Printing Out
Paper as opposed to DOP -- Developing Out Paper.  What this means is
that the image appears as the paper is exposed to light.  Conventional
papers -- the DOP's all form a latent image and must be developed in
chemicals to produce the visible image.  The POP image is composed of
very tiny "golf balls" of silver called "photolytic" silver.  These
particles, due to their large surface to volume ratio.  The silver is in
fact fine enough that it is sometimes referred to as "colloidal".  DOP's
produce a "filamentary" silver that looks more like steel wool bundles
(though not as dense as steel wool).  As the particles are whittled down
to colloidal size, the properties change.  Made small enough, silver can
become a good electrical insulator. Anyway, the change in properties is
responsible for the odd color of POPs vs DOPs.
  
In the early history of photography, photographers were doing all kinds
of mucking around with the fixing agents and washing.  Often they would
purposely decompose the fixer to produce a more brownish tone or they
would only rinse the print so that time and residual chemicals would
produce odd tones. Prints faded very quickly at that time because of
these practices and blue ribbon panel of experts was convened, largely
funded by prince Charles.  The panel consisted of scientists,
photographers, and other experts from various fields.  The panel
determined that the cause of fading in those photographs examined was
because of poor processing.  The panel also noted that even well
processed photographs would fade in the polluted air of 19th Century
London.  All the gases from coal burning was causing severe damage also.
In later years, authors writing about photography ignored the panel's
concerns about pollution and simply wrote about poor processing as being
the problem with all fading.  This myth has been carried over the years
and is still believed today.  Anyway, I digress.  The point is that many
of the early prints WERE poorly processed and there is often some silver
salts still in the prints.  Upon exposure to light, these salts start to
darken and cause silver in areas where it was not wanted. It is not
possible to bleach out these silver particles without bleaching the
image silver and therefore it is permanent.  Some photographs also have
a tinted binder, or hand coloring.  Some of these coloring agents are
also light sensitive-- in fact most tinted albumen photographs (albumen
binder was dyed) have lost their color to light exposure over the years.
You never know if a photograph is sensitive or not.  I recall that a
year or two ago, there was an exhibition up (I wish I could remember
where) that had a problem.  Fortunately, they were monitoring the
exhibition regularly and they spotted rapid image deterioration in one
of the albumen prints. It had been thought to be quite stable when it
was put on exhibit, but proved not to be so.

To anyone who is thinking about attending the seminar, it is bigger at
least longer) and better (we don't leave you in no man's land in
Henrietta) with more participation from the Eastman House.  For the
first time, IPI, Grant Romer (Eastman House) and Debbie Hess Norris are
creating the program.  In this respect, participants will partly be
Guinea Pigs, but we hope to have the most extensive and the best program
ever.

-Doug

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                   Conservation DistList Instance 5:1
                   Distributed: Sunday, May 19, 1991
                        Message Id: cdl-5-1-003
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