Digital BW, The Print

Clayton,

>... Bottom line is all OBAs are not created equal.  Older 
>formulations "burn off" more quickly than newer ones... 

>For example, I have observed in a Condor BW print, an extremely bright
>pure white paper, that after several months of open exposure to room
>light (daylight and fluorescent) the hard edge of brightness lessens
>noticeably ...
>Yet the paper remains a "white" paper, not even close to the cream
>color of most non-OBA papers ...

Interesting issues -- these "OBAs."  

Some of the articles say these should really be called "FWAs" for
"Fluorescent Whitening Agents."  

There do seem to be a number of different types and categories of
brighteners and whiteners. Some appear to be a type of dyes.

I've read of OBAs being referred to as "bad actors" that yellow in old
carpet and other cleaning solutions.  

They were said to be major sources of problems in the original RC
wet-process papers.  The byproducts apparently attacked the polyethylene.
That problem has been said by some to have been cured by better OBAs and
anti-oxidants, that themselves originally yellowed.

The Hawk Mtn. rep referenced an attack by OBAs on dye molecules.  Pigment
colors are often referred to as "dye stacks."  So it seems to me there is a
plausible argument to say the OBA byproducts might also attack color
pigments.

In the past I'd thought titanium dioxide (TiO2 -- in various forms) was one
of these OBAs, if not the main thing that was used.  However, it might be a
"whitener" that is in a bit of a different class.  Or it may depend on its
precise form.  

TiO2 has been referred to as a rather durable pigment that is very important
with respect to paper whiteness and opacity.  When I wanted the brightest
white paint for some project, titanium dioxide-based pigments were what I
used.  In its category it seems to very highly regarded.  It may be a
different category than the FWAs.  

On the other hand TiO2 is not an inert substance.  I recently read, for
example, that titanium dioxide was used as a catalyst for direct
sunlight-to-hydrogen solar power cells.  It breaks water into its
constituent parts. 


(As an interesting aside, these solar hydrogen generators are a very hot
technology.  In a hydrogen economy, we may be fueling our systems from the
hydrogen we generate ourselves. Imagine the ramifications of a
non-hydrocarbon-based world economy where we generated our power on our own
roof-tops.)  (Clear, sunny weather area real estate just took a jump.)


In the paper context, I've sometimes read of OBAs being associated with
producing reactive substances.  

My best fade tests have been with papers that are said to be "OBA" free but
still quite bright, modern paper (UltraSmooth and Premium Semigloss).  On
the other hand, good old EEM was barely behind these papers, and Arches Hot
Press was not impressive in fade tests.  Still, I give top credibility to
the actual experience that extremely old, natural-fiber paper books, written
with lamp black (carbon), can look great.  (My "carbon on cotton" mantra for
archiving.)  Some degree of buffering may be needed and in the best of these
older papers due to the calcium carbonate (or similar substance) that was in
the local water.


Lots of questions.  I'm reminded again that as the size of the spot of light
increases, the circumference of darkness expands.

Paul
www.PaulRoark.com