Digital BW, The Print

>... Does anyone have recommendations for which
>varnishes/sprays are best for both (1)
>increasing Dmax and (2) archival permanence?

There are no 100% answers for these questions.  For Dmax increase, the best
luck I've had is the wire-rod application of water-based, gloss acrylic.
Liquitex and Golden are major suppliers to art stores, where you'll find the
products.  I have also now identified a polyurethane that is supposed to be
free from yellowing (Polyshield by Hydrocote).  Polyurethane may have some
advantages if it does not yellow, but most of the popular ones do yellow.

For archival permanence, don't use anything.  Conservators do not like any
coatings.  (Of course, they also don't like any inkjet products anyway, so
I'm not sure how much we lose by coating.)  Although I recently posted
excerpts from a speech by the National Gallery's Chief of Conservation that
indicated they fix pastels with Krylon acrylic spray (which the conservator
rated at 400 years), Krylon representatives do not have any public data that
supports that.  They make no claims of archival life for their products.
(The Krylon rep could not find any reference to the product number the
National Gallery person mentioned).

At this point, I'm not sure anything more than a light coat of Krylon
Crystal Clear for protection from physical damage is warranted -- and only
where the print is expected to be subject to such abuse.  It lowers the
dynamic range slightly but has no significant visual impact on the print.
In my mind, it is a good idea if the prints are not going to be under glass.
These inkjet pigments are easily marred.

The thicker coatings we are experimenting with must currently be considered
for artistic effect only.  What I hope we get to eventually is an
"encapsulated carbon print" that is so tough that it can be displayed
without glass and has stability that approaches the silver print.  Whether
we get there is an open question.  However, the coatings we have today are
so much tougher than the gelatin of a silver print, that I think there is
hope for a very interesting product.

Paul
http://www.PaulRoark.com