Digital BW, The Print

>... Hahnemuhle White Velvet ... has 25% rag content, but is 
>supposed to be acid free.  Will this be as archival as a 100% 
>cotton paper? I know it has OBAs.  I am currently using 
>photorag with UT2 inks and want to be sure of similair longevity. 

This is an interesting question.  My short answer would be that good
"acid-free," wood-based paper will probably be fine.  Some say that if there
is less than 1% lignin and more than 2% buffering, the paper will be
"archival." 

The long answer is below.

The dogma is the cotton (rag) is best due to its not having any lignin in
it.  Lignin is the hard part of tree wood that allows trees to grow tall.
Unfortunately, lignin puts out acidic by-products as it breaks down.  These
will destroy the paper unless mopped up by sufficient buffers.  Lignin is
also photo sensitive, turning yellow with light exposure whether or not the
paper is buffered.  But then the OBAs burning out with light exposure will
probably be the major source of paper yellowing, and even our carbon
pigments tend to yellow (even if they are not fading).  So, expect some
yellowing over time. 

The issue may be a question of how much lignin and how well it is buffered.
Newsprint is terrible even though it is buffered because it has the full
load of lignin in it, being basically ground-up trees.

Of course, making paper from wood is cheap, and removing lignin costs money.

Alpha cellulose is what the best wood-based paper is sometimes called.  It
is said to be pure cellulose, having had all the lignin removed.  I've heard
contradictory statements from "experts" as to whether it is possible to
remove all the lignin.

Many if not most of the good fiber-based darkroom papers are said to have
had an alpha cellulose paper base.  Because of the acid stop bath, they
presumably cannot have buffering (usually calcium carbonate) in them.  I've
tested my old fiber prints and found that the atmospheric acids from inside
my file cabinet were turning the un-mounted fiber prints yellow.  My Abbey
acid test pen confirmed that they had become acidic.  (Mounting on a
buffered mat board or using buffered interleaving would probably have helped
avoid this.)  

Buffered, wood-based inkjet papers would probably not be as sensitive to
air-borne acids as the fiber prints.  (Epson Enhance Matte is not in this
class, being acidic from the outset and not buffered.)  So, one could argue
that good "acid free" wood-based inkjet paper are more likely to be
"archival" than the old fiber prints.

Although this is speculative, there may be good things that come from
avoiding too much cotton. One has to ask why some if not all of the best
darkroom fiber papers did not use cotton.  Perhaps it was just cost, but
maybe the softness of cotton fibers makes it more difficult to have a
coating stay stuck to the paper.  I suspect the softness of the cotton
fibers is a source of problems.

Additionally, the huge irony may be that lignin turns out to be almost like
a buffer against oxidants and some atmospheric pollution that destroys
paper.  

So ... who knows?  I think excellent paper can be made from trees if
properly processed.  The real issue may relate to marketing and not
longevity.

Paul
www.PaulRoark.com