Digital BW, The Print

>>With glop,

(or post-printing spray, which most will probably not want to mess with,)

>> printing to RC paper is now a practical reality.

>... is the RC paper I keep seeing references to ... resin coated 
>photographic paper (i.e. the kind I used to use in the darkroom ...

No, it's special inkjet paper.  About the only similarity is that it has a
polyethylene barrier between the coating and the paper base.  This allows
for a much smoother surface, and it stops the water in the ink from hitting
the paper, causing the waviness that thin matte papers can suffer from.
Unlike the wet process photo papers, however, the inkjet papers do not have
a back coating or polyethylene.  Thus, for example, the back is open for
deacidification sprays if needed, and the polyethylene will protect the
print from such treatment.

RC papers got a very bad reputation in the wet process darkroom.  I was
burned by the early batches.  They "bronzed" (discolored) with age, the
polyethylene cracked, and they looked plastic.  The discoloration appeared
to be because there was developer in the emulsion to speed machine
processing.  The polyethylene cracking was, apparently, caused by byproducts
of the brighteners used.  They now use different brighteners, anti-oxidants
to mop up the byproducts, and probably a higher grade of polyethylene.  And
the plastic look is now history with the new semi-gloss and semi-matte
finishes.

I prefer to call these new papers "barrier papers."  The real key to them is
the polyethylene barrier between the coating and the paper.  This is what
allows for the smoother surface and big dmax we're looking for.

There is still some uncertainty due to the lack of a long history of
polyethylene use.  However, there is some reason for confidence, even in
addition to the Wilhelm ">200 year" ratings for the Epson Premium line of
papers.

Generally, polyethylene is described as, "a high quality thermoplastic that
has outstanding resistance to both physical and chemical attack.  The
overall general toughness and excellent chemical resistance to a wide array
of wet and dry industrial chemicals and food products make polyethylene
ideally suited for storage tanks and containers."
(http://www.kefco.com/plastics.html)  It is used in medical uses, including
as the bearing in hip replacements, and as packaging for foods.  

So, it appears to be tough stuff that will last a while.  Unfortunately, it,
as well as the sprays we use, are not good oxygen barriers, which is the
next level of protection.

Paul
www.PaulRoark.com