Digital BW, The Print

On 04/01/2008 Clayton Jones wrote:
> Hello Rick,
> 
> >The other significant concern is what this fluorescence does to 
> prints
> >viewed under mixed light sources that contain a strong component of 
> UV
> >(such as daylight). Can you say metamerism?
> 
> Very interesting, first time I've heard of that. I'd love to use a
> non-OBA matte paper but unfortunately I've yet to find one that has as
> good a dmax as HPR and VFA. 

I missed the original, but the idea that OBA's cause metamerism is not 
right. If you use carbon inks on OBA paper, you do not suddenly get 
metamerism. Bromides containing OBA's did not display metamerism.

Metamerism is due to some ink pigments themselves reacting to UV with a 
degree of flourescence, causing a shift in the intensity and/or frequency 
of reflected light, and the image colours to change in an unbalanced 
manner. Such fluorescence can make it hard or impossible to adequately 
profile inks that have this behaviour, as the colour of the illuminant and 
amount of UV changes the image colour balance.

If you use metameric inks on papers containing OBA's you are going to make 
matters a little worse, but the real problem is the inks susceptibility to 
flourescence, not the OBA. They'll substantially do it anyway, even on 
papers without OBA's.

That is *the* issue with printing B&W using CMY pigments, and why 
metamerism is a problem with such inks to a greater or lesser degree. I 
have fairly recently gone from Generations G4 pigments to HP Vivera 
pigments, and the newer HP inks are vastly less metameric, OBA in the 
paper or not.

If you want to check the effects of OBA's, stick a sheet of 
perspex/plexiglass over the print. It blocks UV and you'll see the paper 
and inks unaffected by flourescence of either OBA's or pigments.

You are not going to find papers without OBA's that match papers with 
OBA's for white/brightness/contrast, it's an oxymoron. Paper fibres, no 
matter how pure, just aren't very white. Baryta coating is as white as it 
gets without introducing flourescing OBA's to convert UV into visible light.

The biggest problem with OBA's IMO is that they fade eventually. I have 
some Photo Rag inkjets from 2003 that have sat in striplight and daylight 
24/7, completely unprotected, and the base has turned about the same 
colour as white chocolate. The G4 inks have held up very well.
-- 
Regards

Tony Sleep
http://tonysleep.co.uk