I know Mark is aware of this problem because we discussed it. But I doubt he is in a position to research the reaction, define it, and repost to the rest of us specific results, for all kinds of reasons.
But, this continued confusion that the yellowing discussed here is in any way similar to the yellowing of paper we are used to. It's not the same at all, it's the coating, and it's reaction to certain evaporates and exposure to UV does indeed reverse it, Lero was correct.
Of course there are all kinds of other reasons to keep UV from your art.
A great deal of photographic output over the last several years may be vulnerable because this issue, and others related specifically to inkjet materials, continues to elude the community, even many experts.
Tyler
Hi everyone. Tyler, I'm also aware of the other thread on the yellow staining issue, but have been away from the office in the last few days, so I'm behind on entering these discussions. First, the yellow staining issue is a chemical reaction with some effluent from certain adhesives, and other possible sources of gaseous pollutants. I experienced this problem myself back in the late 1990s on a Lyson paper (rumored to be sourced from Hahnemuhle), but at the time I thought it was a product specific issue originating from a poor choice of packing tape that was use to seal the paper into the shipping package. It affected the top sheet only, and showed up in the print a few weeks after printing, but was unmistakeably in the perfect shape of the "outline" of the tape on the packing box. Since that time, the phenomenon has been experienced by many others, and some even believe that certain "conservation framing" adhesives also cause the problem, although I've never seen the staining problem reported for acrylic "photo safe" adhesives. It appears to be light bleachable when in the distinct yellow condition, but I have also seen yellow-brownish variations that suggest continuing chemical changes which then become incompletely solved by light bleaching. I suspect the bright yellow color is coming from elemental sulfur, and with an appropriate sample of the problem, a chemical analysis using analytical techniques like X-ray fluorescence would zone in on the yellow by-product. Then we could connect that species to the possible reactants. That the manufacturers haven't already investigated and solved this longstanding problem is possibly two-fold 1) the number of incidents that have come to their attention is better handled economically by sending some replacement paper than by going after the root cause, or 2), the root cause has been identified by the manufacturers and possibly determined to be an intrinsic function of the porous silicate microstructure (in other words, it's the nature of the beast).
I could probably talk my former colleagues at the analytical lab at Smithsonian Institution into running such a chemical analysis experiment, but I would need samples with well defined provenance (i.e, what paper and what adhesive was used that caused the problem). And I also need basic funding to pursue these matters and keep my research going, but I'm not a non profit organization, and even if I were, I currently have no safety net (e.g., tenured professor or museum staff position) propping me up financially while I pursue the long and arduous path of seeking grant money to do this type research. Bottom line: without a vibrant membership base at AaI&A, my options are pretty limited, and a large enough base of supporters to carry out this research just isn't there yet. The members I do have in the AaI&A digital print research program are really fantastic, very enthusiastic, and have sent me some very cool samples for light fade testing, so the concept of a subscriber-based research program with members contributing real-world samples for testing does work, but the vital number of members to sustain the effort financially is still a long way off.
As for UV blocking components, either glazings or coatings, here are some basic issues:
1) Coatings have to be very thick to achieve good UV blocking capability. None work as well as a UV blocking glazing such as OP3 plexi. Print shield and other very low viscosity solvent coatings don't create enough thickness to block much UV. You have to apply a thick enough coating that the original surface texture is hidden almost entirely if not completely, and many printmakers don't want to turn their carefully chosen fine art paper texture into a "vinyl placemat". So, the true value of a product like Print shield or Hahnemuhle Protective Spray has more to do with elimination of gloss differential and bronzing, plus it does act to some degree as a gas pollution barrier. I personally suspect that the light fade studies that give such low viscosity coatings positive ratings for UV protection and increased light fastness are actually mis-indentifying what the coating is actually doing. It can impede gas penetration into the microporous coating, and in so doing, slow down oxidative reactions (light fading often being a photo-chemical oxidation reaction) on light fade test equipment that relies on high air flow rates over the substrate to keep temperature in control.
2). UV inhibitors of any kind, whether it be coatings or glazings, tend to shut down the function of OBAs in the paper, so if you like an OBA-containing "bright white" paper for your artistic vision, you are going to have to ensure that UV blocking glazings or coatings aren't added on top of the print in order to get the print to retain the "bright white" appearance you wanted it to have by selecting a high content OBA paper. Yet those UV blockers do extend light fade resistance for the inks, so no free lunch.
3). In order:
Glass blocks out 90% UV energy below about 330 nanometers.
Regular Acrylic - 90% UV blocking at about 360 nanometers
UV blocking (e.g OP3 plexi) -90% UV blocking at about 390 nanometers
UVA energy is considered to be energy within the 320-380 nanmmeter band. Hence, regular acrylic is far superior to glass, and OP3 plexi is far superior to regular acrylic plexi in terms of completely eliminating the active UV induced fading of artwork. However, the mythology that UV is the prime "light fade" inducing culprit is patently false. Blue wavelenth energy, albeit not as chemically potent as UV radiation, is generally available (and required for good color discrimination) at much higher levels than UV when looking at artwork, so its lesser potency is offset to a large degree by its greater abundancy. Bottom line is that even with UV aborbing glazing, light fastness is still an issue for long term preservation of artwork. AaI&A megalux-hour ratings provide a measure of the print's resistance to light induced damage. With decent knowledge of an artwork's resistance to fade, informed choices can be made on how to wisely display any kind of artwork, even artwork that is quite fugitive to light.
Ok, I think I will end there before this becomes a full blown conservation tutorial.
kind regards,
Mark
http:/www.aardenburg-imaging.com