Digital BW, The Print

I haven't tested the hydrocote coated prints, but when I was testing a 
variety of of different acrylic based coatings with piezo inks I found 
that under dry south window testing the coating improved the fade by up 
to 100%...so this is the opposite of Paul's results with the Hydrocote. 
  Honestly I'm still a bit skeptical of the aliphatic polyurethanes 
being as good for paper coating as the acrylics...but this is not based 
on actual comparative testing...just my knowledge of the respective 
chemistries.

Robert


On Saturday, August 9, 2003, at 06:35  PM, Paul Roark wrote:

> 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
>
>
>
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