Digital BW, The Print

I want to correct and expand on my original posting on this InkJetMall test.

The question was:

>> Is there any comparisons available that shows the longevity of 
>>Ultrachrome inks vs. Carbon Inks such as f.ex. MIS Quadtones?

>Inkjet mall's website has a comparative analysis of Ultrachrome, 
>various Piezotone (carbon) inks , Sundance and MIS-FS inks based on 
>1000 hr xenon lamp tests.  ... Here's the link:

>http://www.inkjetmall.com/store/info/1000-hours.html

I originally misread the test of Photo Black to be Light Black -- my
mistake.

However, my opinion of the credibility of the InkJetMall (IJM) test stands
-- I do not believe the results can be taken at face value.  

The IJM text following the numbers states, "UltraChrome inks have fade rates
from 4% - 17% in these Xenon tests.  PiezoTone inks with Museum Black have
fade rates from less than 1% to only 7.3%."

I agree that the current best black and gray inks are more lightfast than
the UltraChrome color pigments.  However, I can't say how much better they
are, and, unfortunately, I don't believe the IJM test shows that either.
So, I still would rely on the Wilhelm test of the UltraChrome 9600 inks,
comparing the color to B&W (which still has color in it) as the most
reliable.  See http://www.wilhelm-research.com/.  That test understates the
differences, but at least I have some confidence that the test was
responsibly conducted.

Of more concern to me is the implication of the IJM test that the PT gray
inks are vastly superior to Epson UC black and gray inks and the UC inkset
in general.

My tests show the PiezoTone (PT) gray and Museum black inks to be about like
the MIS Ultra Tone (UT) inks and UltraChrome (UC) black & light black inks.
They are so close I can't say one is better than the other.  

All three of these inksets are much better than the old quads, including the
PiezoBW (Sundance) and MIS FS inks.  

Let me point out a few things about the IJM test that should raise some
eyebrows.  Starting with the first numbers given in the IJM tests,
UltraChrome Photo Black is said to have an optical density of 1.73 on
PhotoRag -- higher than the matte black.  This is just not believable.
There would be no need for matte black ink if Photo black inks could reach
this density on matte papers.  Typical of what can be expected of Photo
Black is what MIS PK gets of PhotoRag -- 1.38 ("visual density" read by my
X-Rite Digital Swatchbook, Black only printing with a 1280). 

Next, look at the optical densities of the PiezoTone cyan-position (dark
gray) inks.  They are listed as about 0.7.  Yet, if the cyan ink is in the
black position and printed in BO mode, it is over 1.3 on EEM (and I'm quite
sure this is also true for PhotoRag which was used in the IJM test).  If it
is in the color position and printed at full strength, it is just under 1.3
on EEM with an 1160.

So, what did IJM do here?  The IJM notes state, "All of the monochromatic
inks were printed in patches of gray or black.  The color inks were printed
in patches of their full hue."

So, they appear to have printed the Epson black inks at full strength and
printed the PT gray inks at closer to 50%.  IJM omitted testing the Epson UC
Light black ink, which would have been the most similar to the PT dark gray.
To be blunt, this deck appears to have been stacked against Epson.

Now let's consider the light.  This type of extremely bright Xenon light is
heavily used in industry because its brightness speeds up the testing, and
its spectrum is close to that of the sun.  When testing outdoor paints, the
light might be used unfiltered, but to emulate indoor lighting a glass
filter is used to cut the UV and make the light similar to what comes in
through the windows of a house.

The IJM Xenon light was not filtered.  So the light source was
representative of outdoor lighting at best.  It was not representative of
indoor lighting.  Like the sun, the Xenon spectrum has significant amounts
of short UV unless a glass filter is put over it.  Normal glass filters out
the most damaging, short-wavelength UV light.  I'm not sure what affects
this inappropriate light has on the results, but I suspect the UV affected
the color pigments most.  For example, the relative fade rates of the Epson
color pigments are not what I see in my tests or most other tests of color
pigments.  See, for example, the Rochester Institute of Technology (RIT)
test results for MIS Archival pigments at
http://www.inksupply.com/index.cfm?source=html/rit.html.  

Yet, IJM tries to discredit the light sources used by Wilhelm and RIT,
probably the most reputable photographic testers in the world.  

But the UV content is probably not the worst problem.  This light source is
probably so bright that the samples were heated significantly.  Most
importantly, they would be heated in proportion to their density.  I suggest
that this is why the PiezoTone grays were printed at about 50%, the Epson
light black omitted, and the Epson pigs printed at 100%.  The blacker the
ink is, the greater the heat problem.  Heat as well as light will accelerate
the oxidation/fading of pigments.  So, the heat probably disproportionately
affected the Epson inks relative to the PT light gray inks.  

Speaking of light gray inks, the light gray PiezoTone selenium actually had
a negative fade after 1000 hours of this intense bombardment.  That's quite
a trick.  

I was thinking that if there is anything useful coming out of this IJM
"test" it might be the relative fading of the Epson black and color inks.
But, those results are also suspect.  In addition to the UV light problem,
the optical density numbers don't make sense.  The optical density of yellow
is listed as 1.14.  Yet, yellow has the characteristic that it has very high
gamut, but very low density.  With my X-Rite I get a "visual" density of
only 0.07 for a 100% patch of Epson Archival yellow. 

Maybe I'm just misreading the IJM test results, but too many of the numbers
just don't make sense to me.  When that is combined with a test design that
seems to be stacked against Epson, I must say that the test tells me more
about IJM that about the relative merits of the inks.

Paul
www.PaulRoark.com