Digital BW, The Print

Paul Roark wrote:

>>> Have you tried a dark cyan overcoat?
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>>I will try that. But an overcoat of cyan pigment on a black pigment
>>layer isn't producing a black dye layer though.
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>True, it's not a dye.  But if it is truly transparent, then it relies on the
>reflectance of the  underlying substrate -- usually paper.  Here, however,
>that substrate is carbon.  So, its absorbency, the way a subtractive,
>transparent color works, takes out only certain colors of the underlying,
>reflective substrate.  Carbon is warm, so the cyan is absorbing the reds of
>that warmth.  The cyan part of the carbon reflection will come right back
>through, but there isn't much of that. 
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>I guess the question is, in part, how transparent the cyan really is.
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>>One of my concerns with colored overcoatings is that they may increase
>>metamerism.
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>What I saw was so dark if there is some it's not of much consequence. 
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>Only one way to see.
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Paul,

No positive results.

I have printed some proofs with the Epson 10K, WasatchSoftRip, MIS 7600 
inks (including Eboni black) on HPR. Spectrocam Status T measurements.

The RIP was unlinearised, uncalibrated etc for this task, no need for 
that either. Straight CMYK fed it gives straight CMYK output. A square 
with strips descending  from 100% black, 99%, 94%, up to 66% black, next 
to one another. First two prints of that. Forced dried and after 30 
minutes a similar Cyan square printed on the black but 90 degrees 
turned. The other black square was over printed with the Light Cyan 
steps = 50% > 33% C.

The results, less visual blackness, a heavy magenta-aubergine sheen and 
a drop in Dmax of the best black strip (94%) from 1.747  to 1.54 for the 
100% cyan overcoat to 1.65 for the Lightest Cyan strip.

The other way around with Cyan first and black overcoat delivered a drop 
in Dmax of about 0.06 for the heaviest Cyan underlay and 0.02 for the 
lightest Cyan underlay. So no gain there either. Visually a bit bluer 
and lighter, which seems to increase in time, not much metamerism. I 
don't think I will measure them again, there's nothing to win there.

Given the weaving of the Epson head and the color print order the truth 
will be somewhere in between when this is done in one printrun.

This shows how much pigment inks reflect light. It may be different for 
another inkset.

There's one thing we didn't discuss on the differences between dye and 
pigment inks. The dye ink will be more transparent but still have more 
coloring power, I don't think one can put a too heavy load of dye in an 
inkjet ink, it will still print. With pigment inks we are at the edge of 
consistency in inkjet printing, pigment settling and piezo pump capacity 
etc considered. The coloring power of the dye will result in a darker 
coating from the top to the bottom. Less reflection than with pigments 
and heavier filtering inwards.

Ernst