https://caring4art.wordpress.com/2016/09/01/temporary-yellowing-of-inkjet-paper-coatings/
It sums up most causes of paper yellowing. Air pollutants formed by candles and open fires (Xmas time) are a well known source. A thin protective spray layer could help like it does help to reduce oxidation of OBA content, another possible cause of paperwhite color shifts. Framing behind glass protects more though. Aardenburg Imaging has some articles on the subject.
Ernst, op de lei getypt.
The correct term not used in the cited article for the rapid inkjet paper yellowing problem is
phenolic yellowing. I'm pretty sure the major fine art inkjet manufacturers know exactly what it is, but just don't want to say. Phenolic yellowing is a well known issue in the textile industry (e.g. yellowing of white and light colored garments during short and longer term storage in various plastic garment bags). Phenolic yellowing was never an issue with traditional silver gelatin prints, so most photo conservators and indeed, the museum and Archives community in general, is just starting to understand the phenolic yellowing problem with respect to microporous inkjet media.
I mentioned the chemistry "ingredients" needed to cause phenolic yellowing of microporous inkjet papers in an article I wrote a couple of years ago. See the section "Avoid dry mount tissues" starting on page 33:
https://www.aardenburg-imaging.com/wp-content/uploads/2021/04/Aardenburg-Imaging-Adhesive-Free-Picture-Framing-Technique.pdf Basically, one needs to have three ingredients present for rapid yellowing to occur. 1) an alkaline environment...microporous inkjet coatings supply this ingredient because they are quite alkaline by formulation, whereas traditional silver gelatin prints are essentially pH neutral or slightly acidic after proper processing. 2) phenolic compounds, eg., Butylated Hydroxytoluene (BHT) which is used in many plastic materials as an anti-oxidant, terpene phenols that appear to be used in widely recommended photo dry mount tissues (but the vendors won't disclose), and other adhesives to increase adhesive bond strength, etc. 3) NOx, which as you probably know is a gaseous byproduct of fossil fuel burning.
Because traditional photographs use a gelatin binder, the image binder layer is not porous thus it keeps the phenol compounds from penetrating into the gelatin binder, whereas microporous inkjet is exactly as described, i.e., presenting massive surface area at the microporous level to suck up the ink but also making the image binder susceptible to vapor phase deposition of the phenolic compounds. Then along comes some exposure to NOx from our modern industrial society, and phenolic yellowing can indeed appear in a matter of days.
If caught early enough the light bleaching recommendation can reverse it because the phenolic yellow stain is rather light fugitive, but some of my experiments show that in advanced stages the light bleaching trick is not entirely effective. Moreover, if you catch the problem in the early stages and light bleach it away, it can and will return if the causal agents are not eliminated.
Top coats like Hahnemuhle Protective Spray probably help reduce the problem, but I doubt they totally eliminate the phenolic yellowing problem because they don't totally seal the micropores. Harmful gases can penetrate through the back side of a fiber based print, and even from the front since these top coats can't be applied very thick or the desired texture of the fine art media gets altered in a noticeable and usually objectionable way. More testing is needed in this regard.
Lastly, I am working with Henry Duan at the National Archives in Washington DC along with other colleagues at the Image Permanence Institute in Rochester, NY to try to develop repeatable test methods that will help identify which media are more susceptible to phenolic yellowing as well as what enclosure materials are safe to use with inkjet media. It's a challenging research project to say the least, but I think it's the last big issue when we talk about archival inkjet prints. We've tackled light fast inks and long-lasting base papers. Many good fine art papers are now OBA-free (not a single RC paper, though), so one can relatively easily avoid the OBA problem unless you like resin coated(RC) papers. Now we just need to address better non yellowing inkjet receptor coatings, or at least provide better recommendations as to best environmental practices for long lasting prints.
Cheers,
Mark
http://www.aardenburg-imaging.com
Poll
