Digital BW, The Print

ccolbertbw wrote:
> I find it hard to believe that "mixing" the colors in the bottle requires so much less color 
> pigment than separately applied dots that it has a differential effect on longevity. Perhaps 
> it is an issue at the extreme (e.g., very cold where lots of blue is applied), but I would 
> guess that an equivalent cold ink wouldn't have all that much less color pigment. 
> 
> 
> Costa Colbert

My guess is that you need less colorant with an Ultrachrome 
inkset to get a tone throughout the greyscale range than when you 
want to achieve it with a colored quad inkset. Not much 
difference between the two in the shadows but from 50% to the 
highlights the dots are more separated and the separate color ink 
will benefit from the reflectance of the substrate while it isn't 
embedded in a grey ink that will reduce light transmission. Like 
in offset raster screens in the highlights the subtractive colour 
mixing isn't working perfect anymore. The white component starts 
to play a role. Profiling to get the correct (grey) color 
included of course. It has some similarity with the fact that the 
gamut of a CcMmYK inkset is slightly wider than that of a CMYK 
inkset, less white paper reflectance with the first (or as I 
think it should be said, a better subtractive mixing).

That you need less color ink in that range from 50% to the 
highlights doesn't mean that you actually get a better fade 
resistance or less color shift. It is far more likely that the 
print made with the Ultrachrome etc will show a color shift in 
the highlights later on. That's the part with Lc, Lm, Lk mixes 
with the right RIPs and for the Epson driver it is Lc, Lm and Y 
from 20% to 0% as far as I know.

For dyes there's also another thing happening, dyes brought 
together seem to give catalytic fading so in that case it is 
better to make a grey from less components as well. Wilhelm's 
latest PDF on his site.
http://www.wilhelm-research.com/WIR_ISTpresen_2004_02MMG_HW.html

We can't look in the ink kitchens of the ink manufacturers 
either, if a blue toner is made by adding some magenta + cyan dye 
or pigment and not with a single blue dye or pigment then there 
may not be the advantage of the better coloring strength + fade 
resistance of a single hue colorant.

In short I think that a colored quad ink will be better to avoid 
color shifts in time but not because there's less colorant in it !

As usual I'm struggling with the B&W terms for colorants = toners 
etc. If it can be restricted to a purely B&W discussion it might 
work but in this thread it isn't helping.

Ernst