Roger Breton via colorsync-users wrote:
This “phenomenon” of some optically brightened paper having a higher a* component is a mystery to me. To your knowledge, is it simply a function of having added a lot of FWA to the substrate, during the manufacturing process? Such that, as more and more FWA is added, a* simply becomes progressively more positive? Turning into “redder” appearance, visually, at some point?
Note that OBE's can be composed of multiple elements, FWA being one of them. Paper manufacturers sometimes also add "shading agents" that alter the reflectance spectrum in other ways. See <http://www.axiphos.com/BrightnessReview.pdf> So there are a range of possible explanations for a paper having an odd reflectance spectrum. Cheers, Graeme Gill.