Reilly ran a workshop in Pittsburgh for archivists and my college sent me so I was fortunate in being able
ask him questions in person. He has done an enormous amount of scientific research on the archivalness
of all kinds of photographic images and the proper way to store them. I was impressed by the depth
of his knowledge. I actually asked him the question as to what kind of prints were the most archival,
i.e. longest lasting. What he said was essentially what is printed in his book about carbon, gum and
platinum but he also said that proper fixing and especially washing were essential. I asked him what
factors were most important in terms of preserving a photographic image. He said that the most
important was relative humidity (40 - 50%). Second was minimum exposure to light, especially
UV light. So the answer to which process is most archival depends to some extent on if the printer
properly fixed and washed the print and then under what conditions it was stored.
A lot of references suggest that platinum prints are the most archival, but I believe that gum prints are
equal, if not better, than platinum at least as black and white images. However, I do think that platinum
prints have a greater tonal range. In terms of color, I believe thatgum prints are the most archival but not,
of course, as long lasting as black and white, However, might mention than when I visited the Societe de
Francais Photographie in Paris I was allowed,as a member, to view some prints in their collection. There
I saw some gum prints in color by Demachy that were to die for, that showed no evidence of fading.
Bob Schramm
Check out my web page at:
http://www.SchrammStudio.com
> Date: Fri, 29 Feb 2008 18:37:48 -0700
> From: zphoto@montana.net
> Subject: possible answer to archivalness comparison between carbon gum and pt/pd
> To: alt-photo-process-L@usask.ca
>
> I was at the library today and came across Reilly's book Care and
> Identification of 19th century photographs. It was published in 1986, so
> the information could be outdated, and I bet Gawain Weaver on the list could
> say what is and isn't still true.
>
> What I found in there was surprising. It said that platinum was
> "exceptionally" archival, however, the agents we use to develop and clear
> wreak havoc with the paper and thus the support turns yellow or whatnot even
> though the pt/pd layer itself is archival. The image is permanent and
> unchanging even though ghosting occurs--the ghosting is a catalytic action
> that affects the paper in contact with the print but not the pt/pd layer
> itself. This catalytic action does, though, affect the paper support itself
> as well, embrittling it or discoloring it. In other words, the pt/pd
> metallic layer is not the issue, but the paper it is on is and that is
> affected by developers and clears as well as the hastened catalytic action
> of the pt/pd.
>
> Now, carbon (this is what blew me away) is exceptionally archival also, but
> the main problem is cracking of the gelatin layers where they are
> thickest--in the shadow areas of the print. Reilly says since the gum layer
> in the shadows is not as thick as the carbon/gelatin layer, this is seldom
> an issue with gum prints. And gum prints have "excellent image stability".
>
> So one strike against pt/pd, one against carbon, none against gum...
>
> That's all for now, going to go read my brand new copy that just arrived
> from Amazon of Christopher James' new book the Book of Alternative
> Photographic Processes. I see a lot of names in there I recognize!!! :)
> Chris
>
>
>
> Christina Z. Anderson
> Assistant Professor
> Photo Option Coordinator
> Montana State University
> CZAphotography.com
> _______________
>
>
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