This is a reply to a number of comments above.
Moab Juniper Rag is OBA free, but the spectral plot suggests it has TiO2. I don't think TiO2 is cause for concern when there are no OBAs present. It's the combination of the OBAs and TiO2 where the trouble begins. The b* value for Juniper Rag is about 3. So, a warm paper but not by too much.
Innova Exhibition Cotton Gloss (not to be confused with Exhibition Photo Baryta) is OBA free, and the spectral plot suggests it does not have TiO2, but it's b* value is 5.4, so quite warm (like Hahnemuhle Bamboo). Probably a very nice choice for B&W imagery, maybe not so good for color unless the scene is naturally warm light to begin with and not any important robins egg blue, light sky blues, etc. in the scene.
Museo Rag was TiO2 and OBA free with slightly whiter white point (b*=2.4) than Moab Juniper.
Sihl Satin Baryta is OBA free and TiO2 free. It's a true barium sulfite coating, IMO. It has a very good whitepoint color (b* = 1.7 according to Sihl. I read approx. 2.0 in samples I've tested). Mostly special order in the U.S. so a bit harder to buy, but worth considering.
The light induced low intensity staining (yellowing) issue appears to be a problem of having both degrading OBAs and TiO2 present in the media. I will be putting a high OBA content/no TiO2 formulation paper into test soon, so it will be interesting to see if LILIS is still present even though OBA fading will be, but I suspect if it is, it will be much less than in media which has both TiO2 and OBAs present.
When no OBas are present, a spectrophotometer (like the popular Xrite i1Pro2) can be used to indicate presence of TiO2. TiO2 whiteners impart a strong downturn in reflectance starting at around 400 nm and increasing strongly at 390-380nm. When OBAS are present, they too cause such a downturn, so the OBA and TiO2 absorption curves get conflated, and it hard to say whether TiO2 is present when OBAs are also present, except with RC photo media where it's a given that RC papers all rely on TiO2/PE coatings. For full confirmation, I have to turn to XRF to prove the presence of TiO2 on non RC media. I have to rent time on XRF equipment, so I can't do this research on a routine basis because my very limited funding doesn't permit. That said, the next batch going into testing at Aardenburg is going to be emphasizing the so-called Baryta papers, thus I will characterize all the chosen media for the next round of testing both with spectral readings and with XRF. I think there is more to be learned here.
The media manufacturers are understandably not forthcoming about chemical formulations, but we need to know the chemistry in order to correlate it with light fastness results, and to in turn place more pressure on the industry to give us more stable papers in this "baryta" and "traditional fiber" class of inkjet media.
cheers,
Mark
http://www.aardenburg-imaging.com