Mark, where do you find out where the OBAs are located at in the paper? I try to avoid OBAs myself, but so many papers have them that it would help to know which ones are going to fade faster than others.
It's easier to find information on the magnitude of OBA fluorescence than it is to find out where the OBAs are located. To find out if a paper has OBA content and how much it fluoresces I know of only two reliable sources. 1)
http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
and 2)
http://www.aardenburg-imaging.com/light-fade-test-results/
To figure out where the OBAs are located, I rely on a couple of different techniques: First, one can use a blacklight at a fixed distance and compare some known media (OBA-free, Low OBA, moderate OBA, and High OBA) with the unknown media you want to evaluate. The High OBA media fluoresce like crazy and about the only way they can do that is if some OBA is present in the top ink coating layer. With low and moderate OBA papers, they glow proportionately, but it gets a bit trickier to figure out exactly where the OBAs are located. Typically, the Low OBA fluorescence occurs when the OBAs are embedded in the paper core only and not in any top coatings, but some low and more so the moderate fluorescence will occur sometimes when OBAs exist at differing concentrations in both paper core and a sublayer or top layer. And of course, using UV included/excluded measurements taken with spectrophotometers like the iOnePro2 are invaluable in terms of an objective quantification of the amount fluorescence.
Lastly, the way I most accurately confirm where the OBA content is located is to carefully slice a cross-section of the paper and examine that cross-section under a mixture of UV plus raking visible light using a stereo microscope at between 10 to 100x magnification. Additionally, I know from the media technology and construction what layers I should be expecting to see. RC media, for example, will have TiO2/PE layers sandwiching the paper core, and traditional wet process photographs will use gelatin coatings whereas inkjet media will have microcporous layers more often than not. Almost all media will additionally have some anti curl layers on the back side of the media to counteract the forward curl of the hygrocopic coatings on the image bearing side.
I hope to start adding some cross-sectional media studies and surface texture photos into the Aardenburg test reports sometime in the near future. Each of those reports is very time consuming to prepare, so I just haven't stepped up my game so far to include additional aspects of all of these very interesting modern media.
cheers,
Mark
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Mark McCormick
