Re: possible answer to archivalness comparison between carbon gum andpt/pd
OK, but I have seen a lot of vintage carbo prints, in Spain, France,
the UK and in the US. I have never seen one with gelatin *crazing*. I
know that it must exist because Reilly mentions it. But I have never,
ever, seen it.
So there. I don't accept your strike against carbon.
At 6:37 PM -0700 2/29/08, Christina Z. Anderson wrote:
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1986, so the information could be outdated, and I bet Gawain Weaver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
Christina Z. Anderson
Photo Option Coordinator
Montana State University