Digital BW, The Print

Ideally, we would like to be able to find a varnish that will be an oxygen
barrier, but so far there appears to be no good oxygen barrier available to
us.  

I've been thinking of trying a low viscosity, aliphatic epoxy, which may be
the best bet for a better moisture barrier, but even it cannot stop oxygen.
However, to the extent we can stop moisture, we might slow the oxidation
because water seems to be like a catalyst for such (think rust).

I think what the current varnishes contribute most to longevity is physical
protection.  Most of the old photos I'm involved with restoring have
physical damage that is more of a problem than fading.  (Acidic paper is
another issue, but it's easy to solve with acid-free paper.)

Some UV protection is also offered by some coatings and is most important
for outside display and Epson UC inks.  MIS pigments in my tests act as if
they have some UV protection built into the base.  For example, while
PremierArt print shield slows the fade rate of UC pigs about 30%, it's only
10% for MIS pigs.  Of course, on matte paper, the PremierArt Print Shield
lowers the dmax of the print so much I don't think it is worth it,
especially on MIS pigs.  So, I use Lascaux (no UV or longevity effects) for
matte prints.  

The thicker the coating, the more effective it seems to be in some tests.  I
think the Wilhelm tests of the solvent v. water-based PremeirArt coatings
demonstrates this.  While solvent-based UV coatings are generally more
effective than water-based ones, according to the Golden tech rep, the
Premier Art Eco (water-borne) coating appears to be more effective than the
solvent based one.

I tried to see about moisture affects by putting my fader with coated v.
uncoated test strips on a water bath and sealing off its vents.  I was using
polyurethane (PUR) (Hydrocote) at the time due, in part, to PUR being a
superior barrier.  However, the polyurethane-coated test strip did worse
than the un-coated test strip.  In my normal tests with no water bath
polyurethane had no effect.  I believe what happened is that the moisture
got to the pigs through the back of the matte paper and then was not dried
out on the surface by the relatively hot light (not nearly as hot as the
Xenon lights used by many commercial testers).  That is, the PUR probably
trapped the moisture at the surface of the particles and made things worse.
One of the criticisms of fade testing is that they usually exaggerate the
lightfastness due to the drying effect of the light on the surface.  (The
testers who think they are measuring and controlling the temperature and
humidity are not really able to know what is happening at the particle
level.  They are simply measuring the air in the chamber, which I don't
believe tells us that much about the actual surface of the particle.)

So, it's a complex problem.  I think a low viscosity aliphatic epoxy as a
first coat and then a second coat that has UV protection -- in part to
protect the epoxy -- might be an interesting combination.

I continue to search for an oxygen barrier, and some films that might be
applied as laminates may be closes.  However, one tech rep at a company that
makes clear oxygen barriers for food and other preservation purposes says
the problems with them include that they have short effective lives.  As
such, they would not meet our needs for archival stability.  He knew of no
oxygen barrier (yet) that would be suitable for our uses.

Paul
www.PaulRoark.com 





> -----Original Message-----
> From: DigitalBlackandWhiteThePrint@yahoogroups.com
> [mailto:DigitalBlackandWhiteThePrint@yahoogroups.com] On Behalf Of
> scott_now_coming
> Sent: Friday, July 01, 2005 5:17 AM
> To: DigitalBlackandWhiteThePrint@yahoogroups.com
> Subject: [Digital BW] Re: Varnish
> 
> Mainly, sealing the print surface from  oxidation.
> 
> Scott
> 
> --- In DigitalBlackandWhiteThePrint@yahoogroups.com, Louis de Stoutz
> <loudest@a...> wrote:
> > Greetings,
> >
> > it seems that quite a few use varnishes. Sorry if this has been
> > asked/said before: what is the archival aspect of those varnishes? Do
> we
> > have any information about the different makes? I wouldn't like to
> > reduce the life-span of my prints because of the wrong varnish!
> >
> > Thanks,
> > Louis
> 
> 
> 
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