Digital BW, The Print

Steve,

You wrote:

>... has anyone had a chance to evaluate the warm-shift/
>fade resistance of the coated  prints versus uncoated?

The coatings I have tested -- acrylic and polyurethane -- appear to have no
substantial effect on fade and warm-shifting characteristics.  However,
light-box type testing like I do does not hold the humidity at the test
standard of 60%, so the testing may well not show the benefits of coating.

I had thought that the coatings would block UV -- even that produced by
fluorescent lights like in my fader.  However, I see virtually no
differences in my tests.  Note that the shortest and most damaging UV is
absorbed by window glass and the normal glazing materials.  So, for indoor
display, I see no reason to use any special UV absorbing materials.  If
applied in a heavy coating, the UV-absorbing materials are just too yellow
to use anyway.

I had also hoped that the coatings would block the oxidizing gases.  My
tests, however, do not provide any evidence for this.  This may or may not
have any meaning.  However, I now suspect the coatings do not accomplish the
goal of being a gas and moisture barrier.  I speculate that the coatings
just lay on top of the pigs, and the gases and moisture enter through the
matte paper.  (I am curious if coatings on a barrier (RC) paper do any
better.)

I must say, however, that I think the simple light-box and south window
tests are inadequate to compare coated pigments and uncoated ones.  My
readings suggest that the heat from the bright light in accelerated,
light-box testing artificially dries the particles.  Thus, any benefit from
coating might not show up in the tests even if it were very significant in
typical real-world display.  Moisture appears to be an important variable in
the fading rate.

I suspect that at the level we are now approaching -- 100+ year, pure
pigments -- the very expensive, Wilhelm-type testing is going to needed to
see the differences in these products.  The simple light boxes that most
have are a fraction of the cost of the machines that hold the humidity,
temperature and other variables where they really need to be.  As such, I'm
becoming inclined to just roughly categorize a material as probably a "class
A" (about probably in the "100 yea" class) -- or not.  I'm not sure our
cheap light box testing is doing much more than showing whether there is dye
in the mix.

(Kodak and others have materials on accelerated testing that suggest our
simple testing may be useless for evaluating relative lives of non-similar
materials -- photo v. inkjet and even coated v. non=coated particles.
Different materials have different reciprocity failures and react
differently to the various fading factors.  A test that just looks at a
single factor may totally miss the actual, real-world performance
differences.)

The good news is that the coatings really to seem to give physical
protection and enhance dmax.  They appear to be neutral on most fade tests.
On some the coated midtones do a hair better, but on some the coated black
pigments do slight less good (perhaps the higher dmax causes the absorption
of more light, generates more heat, and makes it more difficult for the
particles to dissipate the heat).



>... I'm debating whether
>to buy a 7500 and sell my first digital prints through a designer. ...

I just bought a 7500 and think it will make a great B&W machine.  I'm
currently planning on using the coated Epson Archival black pigment mixed as
an FS/Piezo-compatible "quad."  I'll print with the Epson driver an use the
double-cyan ink placement method.  (In short, I'm going to go with the
Epson-coated pigs rather than rely on post-printing coating to protect the
individual pigment particles.  Whether I use post-printing coating for dmax
and physical protection depends on other factors.)

My initial tests with color ink in the 7500 convince me it was an awful
color printer.  Maybe professional profiles help, but for color printing I'd
pay the extra and purchase a 7600.

Paul
http://www.PaulRoark.com