Digital BW, The Print

jeffmoore17@... wrote:

>1) Has anyone done any testing on the issue of whether or not coating
>with a product such as Hydrocote Polyshield affects the archival
>properties of Piezography carbon prints?

I've fade-tested coated v. non-coated prints.  I assume the MIS and Piezo
inks are about the same.  In general, the coated blacks faded a bit faster,
although I think that could well be due to the higher dmax raising the
temperature (by absorbing more light).  The black ink in the test was the
MIS VM-K (probably the same as PiezoBW K).  The 50% patches were generally
the same in terms of their fade rates.

There was one other situation that seemed to accelerate the coated print
fading.  I tested one group under very high humidity conditions.  (The test
light, etc. were right over a tray of water.)  The coated print did fade
faster.  The uncoated prints faded at essentially the same rate as the
low-humidity tests.  I speculate that the difference could be that the hot
light artificially dries the un-coated prints, whereas the coating traps the
water around the pigments.

In general, we've always been led to believe that high humidity accelerates
fading, but this has never shown up in my tests except for the coated
prints.  One of the criticisms of accelerated testing is that it
artificially dries the inks, with the result that the fade rate is reduced.

So, I have 2 test results that seem to favor un-coated prints.  I'm very
suspicious that both are more artifacts of the testing than predictors of
faster fading for PUR-coated prints.

>2) When coating Piezo prints with Hydrocote, after a good curing
>period, can these prints be drymounted, i.e., Seal tissue and
>drymount press?

Yes, I've used Seal Colormount at 180 degrees f.  Be sure to use fresh
release paper and wait the full 7-day curing period.  Also, with trimming
the prints, a rotary trimmer might be a good idea.  I've noticed a bit of
edge roughness when trimming with a straight razor knife.

As an aside, one of the PUR experts told me that heat accelerates the
cross-linking and curing.  Heating the PUR soon after application might
actually make for stronger coating -- bringing the strength/extent of
cross-lining of the single-solution, water-borne products close to the
industrial products.  (The adhesion of a water-borne PUR will not, however,
match the solvent-based products.)  This heating information suggests that
the use of a hair-drier might not only speed the drying and curing, but also
result in a stronger coating.

Paul
http://www.PaulRoark.com