Digital BW, The Print

Hi Ernst,


>> Take a close look at the charts at the bottom of
>> http://www.paulroark.com/BW-Info/4K+.pdf , ...
>> I'm not sure there is any way to solve the separation 
>> problem not only in a large format printers but also 
>> in continuous feed systems.

> ... Strange enough I could keep 
> a sepia mix of the old Epson Archival pigment
> LM + Y very stable ...  About the only ink that remained stable.

I'm suspicious that the separation issue could be less of a problem with
coated pigments.  One person I discussed the issue with felt that what was
going on was differential affinities among the particles and materials used
in the printers -- in particular the tubing.  I don't have enough chemistry
background to evaluate this, but I think what he was saying is that the
different types of pigment particles have different electrostatic
attractions to, in particular, the material the tubes are made of.  Perhaps
the coating tends to equalize this???  This theory is obviously speculation.


I tend to simply focus on the bottom line.  Although I was able to reverse
one tone shift by altering the base formula, when I corrected for one Lab
axis, the other one became unstable.  I concluded that with enough time I
could probably achieve a reasonable balance for an ink that had 2 different
pigments in it, but the addition of a third pigment type probably would make
the job virtually impossible.  

As a practical matter, life is too short to mess with this problem.  The
printers are now good enough that the marginal improvements in smoothness
and even more marginal (if any) improvements in lightfastness of the blended
inksets are, for me, no longer worth the cost in terms of stability,
inability to select the best pigment for each spot, and QC issues.  Frankly,
I also found that it was simpler to profile rip systems with non-blended
inksets.  So, while I think the C88 EZ, R2, and other desktop monotone
inksets are worth the effort, the UT-3D is probably my last blended variable
tone inkset.  

Particularly since I expect the 3800 - a large format design - to grab a
significant part of the serious amateur photo market, I don't want to have
the stability issues come back to haunt me on the scale I expect that
printer to be sold.  Current large format printers in the hands of service
bureau experts who use the machines regularly minimizes the problem.
Imagine the magnitude of the issue if legions of amateurs have 3800s sitting
idle most of the time with a blended inkset.    

Marketing a pre-filled continuous flow system with a blended inkset through
retail stores, where the units sit on the shelves or in inventory for weeks
or months, is also not a position I'd wish on anyone.  The blended inksets
in large format or continuous flow systems only work well when they are
regularly used.  My experience is that when they sit idle the inks separate
(and worse in some continuous flow systems).

Paul
www.PaulRoark.com