Digital BW, The Print

> I believe I recall the primary problem with optical brighteners in
> paper being that they have a tendency to lose their whiteness over
> time.

Yes, the affect on the pigments or paper other than the color of the paper
is not clear.  Some of the older OBAs apparently had reactive byproducts
that attacked the image or substrate (like the original RC papers).  On the
other hand, some brightened papers do very well on Wilhelm tests.


> I'm assuming this shows up as "yellowing", ...

Yes, the yellowing usually occurs relatively early in a fade test and then
stabilizes.  I think the following spectrophotometer Lab (a, b) numbers from
an EEM fade test are typical:

Before fade test EEM paper white (a, b) = (1.26, -3.82)

After the fade test (a, b) = (-0.89, 3.70)

I believe this is a delta E of 7.8.

The most obvious change is along the "b" (yellow-blue) axis, with the paper
going from -3.82 blue to +3.7 yellow.

So, the paper starts the fade test looking bright white and ends the test
looking like one of the non-OBA, "natural" papers.

I like the natural papers, which stay essentially the same in these tests.
I personally don't like the way the brightened papers look (too cold) next
to my matte board.  Additionally, however, I don't like the idea that
someone might open up one of my matted prints and see a "shadow" from the
over-matte.  The yellowing of the paper will not give a feeling of
confidence in the quality of the materials.

Paul
www.PaulRoark.com