Re: possible answer to archivalness comparison between carbon gum andpt/pd

[Gawain Weaver <gawain.weaver@gmail.com>]

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
gmwipi@rit.edu




On 2/29/08 8:37 PM, "Christina Z. Anderson" <zphoto@montana.net> 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 the information could be outdated, and I bet Gawain Weaver on the list could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
> _______________ 
> 
>