Re: possible answer to archivalness comparison between carbon gum andpt/pd
I assume that gelatin crazing (or cracking) results from unstable storage conditions where the temperature and humidity change a lot over short periods of time. It is easy to understand how this could result in gelatin crazing. Unfortunately carbon printing was not all that common in the US, outside of certain large markets in the East, so you don't see too many vintage carbon prints relative to other types of prints.
Just wondering how many persons on this list have actually seen a carbon print?
At 8:04 AM -0500 3/1/08, Gawain Weaver wrote:
Christine-In the spirit of full disclosure I have spent the last 2 1/2 years associated with IPI as a fellow or researcher, so I'm hardly impartial, but I agree with everything (more or less). The original statement that gum is not archival is clearly wrong (I don't think that was ever a point of contention here), however, as was pointed out in the last archival go-around, archivalness is not a useful measure when speaking of the permanence qualities of various processes, and I don't think there can be any one correct answer to the question The degradation processes of platinum are very complex and not fully understood. I suspect even Mike Ware would agree. And the fact that platinum is not one process, but a vast array of possibilities and varying processing solutions, only makes it worse. Platinum does appear to have a catalytic effect on paper, though in well-made and stored prints it does not seem to affect the paper support--only paper stored in contact with the print. The developing agent is not generally a problem, but of course, hydrochloric acid (when used for clearing) is very damaging to paper. Residual iron also appears to cause both staining and paper degradation, but again, the problems are complex and not well studied. The most amazing thing to me is that Sandy and others, who have no doubt seen far more carbon prints than I, have never seen cracking in the dmax areas. This has been so common in my experience that it often useful for identification. It doesn't always happen by any means, but I have seen more prints with cracks than I could count. Gawain -- Gawain Weaver Research Assistant Image Permanence Institute w.585.451.4363 email@example.com On 2/29/08 8:37 PM, "Christina Z. Anderson" <firstname.lastname@example.org> 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 recognize!!! :)Chris Christina Z. Anderson Assistant Professor Photo Option Coordinator Montana State University CZAphotography.com _______________