Amin Gharehchaie wrote:
I bought a package of permajet sample papers and there I tried a paper that permajet says does not have any Optical Brighteners, but Argyll tell me that the FWA content = 0.637455
Argyll uses a heuristic to estimate the FWA content. Without measuring with and without UV illumination, it's not possible to make a definitive conclusion about FWA content. The spectral shape of the paper you are using has a rather "rounded" spectrum into the blue, and the heuristic doesn't do a very good job of estimating the presence of FWA, since it is expecting white paper, with a more straight line characteristic. You really need to examine the spectrum of the paper to make a judgement about whether FWA compensation is going to be appropriate of not. This is pretty easy to spot visually, but paper with odd spectral characteristics (tint) will fool the algorithm used.
From what I can understand is that the optical brighteners are actually inthe ink and not the paper, and Gretag checks only against the paper but Argyll checks against paper and ink.Is this a correct assumtion?
No. Nothing in Argyll will help you if you have ink that fluoresces. You need a quite different instrument and software to deal with such a situation. Graeme Gill.