QTR-Quadtone RIP

Hi Mark,


> In the PDF, you note that:
>
> `If the LM fades faster than the LC, the print will take on a green hue
> that most viewers find rather unpleasant. How well matched the LM and LC
> color pigments are in terms of their rates of fading becomes a significant
> issue for image stability.'
>
> Seems like a big caveat. Is it possible to quantify or mitigate the risk
> here?
>
In terms of quantification, I'd assume the testing of the Piezo inks at
http://www.aardenburg-imaging.com/ are about the same as what you'd see
with MIS blended B&W inks.  In my less stringent testing early in the game,
I found MIS and Piezo inks about equal.  Most casual printers will probably
never notice the shifts.  On the other hand, some of those test prints
turned in a negative Lab A (greenish) after an exposure equal to 3 years of
commercial gallery light level.  I would be hesitant to have my reputation
depend on that type of performance.

On the other hand, I will have show based on the  Epson Noritsu (Claria)
dyes that are clearly not in the 100% carbon league either.  I'll have lots
of materials that make clear the distinction between the media, however.

How to mitigate the color shift is not totally clear.  You can see if there
are tests of prints with protective sprays that help.  Oddly, sometimes a
spray affects one color so much more than another that the color shift
becomes worse.

My answer for high end gallery quality work is to avoid third party color
pigments.

Note that for the color settling issue, I did not test whether agitation of
the wide format carts took care of the problem sufficiently.  With Eboni
the changes in the wide format tubes and dampers seems to be alleviated by
the motion of the head and tubes.  I'm not sure that will be the case with
the color separation.

Overall, my last solution for glossy pigment prints was to go with MIS
carbon in most channels and tone with Epson LM and LC.  See
http://www.paulroark.com/BW-Info/4000-5K-Plus-cmy.pdf

Then again, I've all but abandoned pigment glossy printing. For high end
work, I think matte under glass works better, and for pure high impact,
dyes win.

> I'd probably be using Canson Baryta Photographique, so presumably
> a fair amount of LM and LC would be needed for a neutral print.

Yes, carbon on glossy paper is very warm -- what I call "sepia" tone.  It
takes a lot of color to overcome that degree of warmth.  If you look at the
Aardenburg testing, the Epson LC and LM seem to resist differential fade
the best.

Note that I think the HP Z3200 grays are the best neutral/cool inks.  If I
were designing a gray ink with that type of R&D available to me, I would
not use the C and M that are in the color positions. The ideal color toner
in terms of color shifting is a single pigment that offsets the carbon
warmth.  That way the fade path is a straight line back to the carbon
warmth.  I've actually printed with such a color -- indanthrone blue.  But
it was not properly prepared for inkjets, and the third party B&W volume is
not sufficient to justify the cost of doing so.  There are also issues of
color constancy & metamerism that might affect toner pigment selection and
are much different than what one would want in the color positions.  HP and
the other OEMs have the volume and expertise to do these things.  It would
surprise me if they are just using their color C and M pigments in their
gray inks.

Being stuck with existing third party color inks for toning when doing the
MIS designs, what I did was switch to the R800 blue instead of the magenta.
 This narrows the angle between the color toners and helps to some degree,
but not really enough for a huge impact on the problem.

Sorry I don't have a great, 100% solution for you.  With third party B&W,
blended color + carbon inks I'd test whether agitation is sufficient to
avoid the color drift from settling in wide format printers, and I'd simply
assume that they are not a top collectible or museum grade print.  That
said, they are fine form casual printers and should not show much change in
normal household lighting for a number of years.

Paul
www.PaulRoark.com

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