Digital BW, The Print

> So how or why is there a distinction made between a 'good' photo
paper and, for example a good fine art paper? I thought it was simply
a matter of choice of finish - look and feel. Or is there more to it
than that?
> And when does a need arise from that for museum or archival quality
paper?

Certainly there is some subjectivity in the definitions.

By most accounts, a paper should at least be acid-free to be
considered a fine art paper. Many "photo papers" with an RC base are
not acid-free; the paper base may be acid-free, but the coating is
often a little acidic (this apparently helps to hold the ink better).

Of course, longevity is also an important concern. Unfortunately,
there is very little concrete longevity data (i.e., zero data)
available for most papers. Photo Rag 308 and Innova Smooth Cotton are
pretty popular papers, but to the best of my knowledge there isn't any
longevity data available for these. Most people say, "oh, these should
definitely be in the ballpark of other similar papers for which we do
have information, like Velvet Fine Art or UltraSmooth Fine Art" but
frankly, from a scientific point of view, this is just speculation. 

Paper weight and thickness also come into play. People generally get
the feeling that a thin, reflective paper that has a similar look and
feel of a Costco/Walmart print doesn't go into the same category as a
thick, heavyweight (possibly textured) paper. Papers like Enhanced
Matte (even if it was acid-free) might not go into the "fine art"
category just because they're relatively thin and don't feel "as nice
in the hand" as thicker, heavier papers such as Velvet Fine Art or
Photo Rag. Again, this is subjective.

The presence of optical brighteners (or the lack thereof) is another
point of debate. 

If I had to summarize, I'd say that a paper is considered to be a
"fine art paper" if it satisfies:

  - acid-free and lignin-free

  - made of cotton or alpha cellulose (or some mix of the two)

  - has a suitable thickness/weight (typically at least 14 mils and at
least 250 gsm or so)

  - doesn't contain optical brighteners (widely debated)

Eric