Robert, Thanks for the note. I can't believe I'm about to ask this, 
but....."DO ESFA SHEETS HAVE OPTICAL BRIGHTENERS IN 
THEM....?"

[...]
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[RESPONSE FROM ROBERT:]

Thanks for asking, and allowing me to self-promote:
Crane papers (whether ESFA, ETFA, or MUSEO) do NOT (big 
capitals) have OBA's.  In fact, Crane papers are the only fine art 
digital papers currently being sold that do not have OBA's.
Oops, maybe not the only...the Schoellershammer papers claim 
not to have OBA's.  I don't know about Hawk Mtn papers; I only 
have really seen/tested Osprey, which has a creamy paper base, 
and very white coating, so there may be OBA's in their coating, i 
don't know, and don't want to claim anything until tested.  Oh, and 
concord rag due to its creaminess, i would presume does not 
have OBA's.  I do know that somerset enhanced, all the 
hahnemuhle papers, the brightcube eclipse do have OBA's.
regarding the paper base, the yellowness depends on the 
cleanliness of the raw materials, etc.  concord and arches are 
fairly creamy, Museo is much whiter.  this has to do with the 
cleanliness and nature of the raw materials being used and 
chemicals being added to the paper making process.
being a self-serving, self-promoter, i would say that yes, OBA's 
are causing more harm than good.  but there are people who 
like really bright white and cool tones (eg Jerry Olsen) who may 
be able to figure out how to work with these papers.  David 
Stock's suggestion of framing behind UV glass is a good one 
and MAY help alleviate the loss of effectiveness of OBA's.
[...]

sincerely
robert