#! fwiw I don't know of a more reliable source than Red River for this kind of information. Do you?
Link if you do know of anything better or forever hold your peace.
Hi, I did read your linked article, which in turn linked (under "Resources") to the "better" sources, in my view. One of them, the Image Permanence Institute, at RIT, apparently does the actual testing for the Red River people. Who in turn give a simplified version of the results, as a "worst case" display lifetime.
#2 nobody (apparently) knows anything about the archival nature of silver/gel or other analog prints made by photo labs OR home fanatics (we've just believed that lots of washing would make prints eternal). Smithsonian makes claims. Do they apply to your silver/gel prints?
I spent a number of years as the QC manager in the processing lab division of a large US studio chain. Our goal was along the lines of best possible quality at a price point, always shooting on the Kodak professional portrait color neg film of the day, printed onto an appropriate professional paper (not necessarily Kodak).
At some point, maybe around 1980, the company realized the possible ramifications of making a bad choice in materials, especially given that we had a 100% satisfaction guaranteed policy. So if we selected a paper with poor longevity it could be a very costly choice. Or even some sort of processing issue that could affect Image stability.
So, under the advice of a guy on the ANSI Image stability committee (name of Henry Wilhelm) we set up an abbreviated image stability testing program. About twice a year we ran a set of tests, for both light AND dark fading. I say abbreviated because a proper dark-fading test would be run at perhaps a half-dozen different temperatures. (This allows predictive time to age.) But given the expense of these temperature and humidity controlled test chambers, we elected to use only one, limiting us to comparative tests, only, with no predictive capabilities.
For more info on the dark-fading test procedures, see Henry Wilhelm's book (free download from his website), p. 177 and 178. Charleston Bard et al of Kodak first published details of this so-called Arrhenius test about 1980.
We also ran a light-fading test at the same time. Again, plenty of detail in Henry's book, see Chapter 3.
Over the years we looked at both dye-sub printers and various inkjet type printers, largely for consideration in studio use. If something was worth looking at we'd print test samples asap in order to get the image stability tests started. They'd take perhaps 4 or 5 months for meaningful results. This would be reading a series of test patches every week or two, depending on the rate of change. One set in the heat chamber, one set in the light chamber, yet another in a file cabinet (as a room temperature reference) plus a master reference, kept frozen. And each new media test would be accompanied by at least one known reference - our current production material.
I realize that this doesn't help the typical photographer, say users of this site. I'm mainly responding to the "nobody knows anything" comment. But it gives people a sense of what might be happening in the processing industry. For a more typical photographer I'd suggest to rely on the vendor of materials that you wanna use. Just ask if they have any image stability data on their materials. Or see if either Wilhelm or Ardenberg has tested same - see their websites. If no tests you're on your own. But... if the vendor has a handful of requests perhaps they'll commission a test from RIT. Who knows? In our case, we mostly stuck with major manufacturers - if something went wrong we wanted the strength of a major manufacturer standing behind us. That is, if THEY supplied defective material then they would be expected to help cover the costs of replacing customer work.
One last comment on light fading... this is such an unpredictable situation. In the case of DARK fading, it's fairly simple to predict for a certain storage temperature (and controlled humidity). But for light fading one may not be able to predict the light levels. In one case perhaps direct sunlight comes through the windows at certain times of the year. Or perhaps contaminants in the air affect the print. So the conditions may be too variable to give a good prediction of print life (however that may be defined).
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