Epson Proofing Paper White Semi-Matte? The one this test is based on;
http://www.aardenburg-imaging.com/wp-content/uploads/2015/11/AaI_20140217_SN001Lf.pdf?x18545
It does not have OBA content according Mark's measurements and I have not measured it either. In the AI normal test the white is one of the most stable and what I recall is that it did not have the dark/exposure issue either.
I wonder however whether Mark has new evidence of OBA in that paper or phrased the following a bit odd:
"Epson Proofing Paper White SemiMatte. Epson’s proofing paper differs from the Canon and Epson photo luster media because it contains no OBAs in the PE layers, only OBAs in the paper core where they are more isolated from direct light exposure and also certain light- reactive aspects of the PE/TiO2 chemistry".
It suggests no dark storage issue BTW but I also do not see a higher OBA effect at the back of that paper in my spectral plots. I know the limitations of my measurements (UV light wavelength limitation) and am aware of the UV absorption as shown in the spectral plots. For which I have no sound explication other than a possible high TiO2 content. Could be that the back has an opaque white PE layer instead of the transparent one usually found there.
There have been papers made by the late Ilford that were constructed like Mark describes here for the Epson paper. Whether the more recent Ilford variety is similar I do not know. For the last green plots in the attached image, red for the old one.
The Canon Heavyweight Satin that had good AI test results could have the dark storage problem though. OBA effect at the front even slightly higher than at the back. check the other attached image.
Met vriendelijke groet, Ernst
http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
November 2016 update, 700+ inkjet media white spectral plots
As many of you know, RC media are comprised of a typical base paper sheet sandwiched between a top and bottom polyethylene (PE) layer. Titanium Dioxide (TiO2) is used as the whitening agent and embedded directly into the Top PE layer, sometimes but not always in the bottom PE layer as well. The image forming layer(s) (ie., gelatin layers for silver halide RC photo, or inkjet receptor layers for inkjet RC photo paper), are adhered to the top PE/TiO2 layer. Adhesion of the image forming layer to the PE/TiO2 is one of many problematic aspects of RC media for long term stability, but let's leave that issue out of the discussion for today. Anticurl layers are also typically used on the verso, ie. adhered to the bottom PE layer.. Unlike the vast majority of the RC media sold as photo papers, the Epson Proofing Paper White Semimatte (EpPPWSM) is free of OBAs in the image forming layer, and more importantly, also not included in the top PE/TiO2 layer. There are OBAs contained in the base paper sheet, however, but the PE/TiO2 layer has very strong UV absorbing opacity such that any OBAs in the base sheet hiding below that layer aren't activated very strongly and have very little effect on the whitepoint properties of the RC media. Thus, when Ernst and I measure the media whitepoint reflected spectral response of EpPPWSM that hiding power of the TiO2 largely prevents the UV fluorescence of the base sheet OBAs, and our instrumentation reads an "OBA-free" response. However, if you cross section the EpPPWSM paper and view under a microscope, you can see that OBAs are present in the base sheet.
Probably because the EpPPWSM paper has no OBAs in the ink receptor coating nor in the top PE layer, my informal studies of the light induced staining phenomenon to date show none of the light induced yellowing exhibited by numerous other popular RC photo papers. I have heard of one anecdotal report from photo conservation colleagues of EpPPWSM exhibiting some yellowing in a dark stored environment, and if that report is true, it is undoubtedly caused by air pollution rather than light induced since the product had been in dark storage from the start. I have not been able to replicate the gas pollution issue, but many microporous inkjet media exhibit yellowing sensitivity to various air pollutants, so I don't think the the air pollutant issue is unique to the EpPPWSM. My own oldest samples of dark stored EpPPWSM paper are now over 3 years old, and the still look and even print as new.
There is quite a range to the magnitude of the light-induced dark storage staining problem, with some papers like Epson Premium luster and glossy RC media examples developing high stain levels after light exposure tests, whereas other media like the now discontinued Canon Heavyweight Satin photo paper or Kodak's older formulation of its Kodak Professional Luster paper exhibit far less stain. Unfortunately, after the Kodak bankruptcy, its inkjet media was picked up by BMG, and the recent marketing literature suggests it has been reformulated. Among other attributes is now the claim of "brighter white", which is often marketspeak for more OBAs, so the Kodak Professional Luster paper needs to be retested. Fuji Crystal Archive II paper, a traditional wet process RC photo paper, lands some where midrange in the levels of stain I've measured to date after the light fade test samples were retired to dark storage for several months or more. The fact that both silver halide wet process papers as well as inkjet paper exhibit the light induced post-exposure yellowing problems in subsequent dark storage indicates this staining phenomenon is not just an inkjet paper issue nor can it be blamed entirely on residual color coupler staining or poor processing in the wet process media as many conservation specialists have long thought when encountering subsequent yellowing problems in traditional RC photo media.
The samples I already have in testing of EpPPSWM to date remain free of any measurable light induced yellowing, thus strongly suggesting to me that this light induced yellowing issue can quickly be reverse engineered by RC media manufacturers if they become more aware of the problem. I think at this point in time they simply aren't aware of it, because a typical lighfade test or a dark stored thermal aging test won't trigger the problem. One has to do a combined light and dark stored testing sequence in order to observe the problem. Much more research to do. The latest round of testing at Aardenburg Imaging is being performed with newer and much faster i1Pro2 instrumentation which will help us track more samples of the same media including dark storage controls, and other samples retired to dark storage after specific light exposure doses have first been applied. Hopefully, this new and ongoing research will begin to give the printmaking community better information on choice of RC media and ultimately lead to an industry solution to the problem as well.
cheers,
Mark
http://www.aardenburg-imaging.com
