Actually, I must correct myself.
I recalibrated the Spyder and now, the values are different. Last night something must have gone wrong when I did the white calibration.
The low OBA paper now also has a negative b-value. I just remeasured it. But it is around -0.5 to -1.
I profiled a paper the other day, that had a b-value of -7. Here it was obvious what to do --> zero b-value and absolute greys.
I am not so sure what to do with the low OBA paper now. I will try and see. It seems that even slight amounts of OBA will result in slightly negative b-values.
The dilemma I am facing is basically this:
For high OBA papers, which appear as bright white to the human eye, it is no problem to set the b-value to zero (paper color is white) and to use neutral greys.
For this low OBA paper that I have it is not as easy because it appears like a warmtone paper to the human eye. So if I zero the b-value, the soft proofing paper color will be off. Furthermore I would like to use the paper greys and not absolute greys but I am not sure if this will work correctly.
A scary Spyder indeed.
Today I measured the Hahnemühle Photo Matt Fibre 200 gsm version and its dual sided version. As I suspected the same papers Innova first introduced as Decor Art IFA24 and IFA25 . The dual sided paper also appeared as Harman by HM Matte Fibre Duo 210 gsm. The spectral plots of 4 clones are in the latest SpectrumViz, AlphaCellulose>Matte Light Textured map.
With an Eye 1 Pro that really measures down to 380 NM wavelength I do not see signs of OBA, not in the spectral plot, not in the Lab numbers that are 97.8 -0.3 1.9 for the Hahnemühle Photo Matte Fibre 200 gsm.
Like with more meters that do not really measure down to 380 NM the Spyder most likely does an educated guess based on the measurements above 400? 420? NM that there is OBA aboard when the L is as high as it is in this case. Few papers go that high without OBA content. Canson Rag Photographique, also without OBAs, has a similar white reflectance and spectral plot.
So consider it a paper without OBAs and check SpectrumViz in the future if it is unclear whether a paper has OBAs or not.
Edit: Innova's specs say No OBA, Keith Cooper's review of the Innova version says No OBA. Hahnemühle's specs say Low OBA for both the HM and Harman by HM version but Hahnemühle has PhotoRag also in the Low OBA category which actually has a Low OBA content. I put all the papers mentioned here + a sample of Canson Rag Photographique under a UV light and the only one that reflects a brighter blue white is the PhotoRag sample.
I do not have the Tecco one but it would not surprise me if it is the same, there must be a source all the brands get this paper quality from.
Met vriendelijke groet, Ernsthttp://www.pigment-print.com/spectralplots/spectrumviz_1.htm
July 2013, 500+ inkjet media white spectral plots.