Re: Gum Tri-Color

I think I'm caught up with this thread now, and I have a couple more
coments from the parts of the discussion I'd missed before:

(1) I had to smile at Tom's reluctance to use the PR209 because it was
called "red" instead of "magenta." As I said earlier, while printers'
inks are labeled "magenta" and "cyan" we don't have pigments that come
labeled that way to make it easy to choose process colors, and are left
to guess what colors might work best, and the ones that work might be
called about anything, but are very seldom called magenta or cyan.
(Well, there are paints that are called "magenta" but that doesn't mean
they are the right color for process magenta, as I will show in a bit.)

As an example of the confusion that prevails on this subject, a quick
look at the recommended pigments in one gum manual alone shows the
following paints being recommended for process magenta: Linel Carmine
Permanent, Linel Ruby Red, Winsor & Newton Alizarin Crimson, and Winsor
& Newton Permanent Magenta. The first two are PV19 (gamma), the rose
quinacridone. (And no, I don't know where the name quinacridone comes
from, but maybe that's one reason I don't use any quinacridone pigments:
don't like the name ;^)) The third is of course PR83 alizarin crimson, a
fugitive pigment that is more crimson than magenta. And the last is PV19
beta, a very blue-violet pigment. So on one page, a gum expert has
recommended three different pigments of very different hues for the
process magenta, none of which match the reflectance profile of process
magenta inks.. Alizarin crimson, which has probably been recommended the
most for a "process magenta" over the years, is the least like a process
magenta in its reflectance curve, having no peak at all in the violet or
blue part of the spectrum. The PR209 I suggested the other day is a
better match than either the PV19 rose quinacridone or the alizarin
crimson; the PV19 has too much of a peak too far in the violet region
and the alizarin crimson has no peak in the blue-violet region. The
PR209 has a low peak, still more violet in hue than the blue-violet peak
in process magenta, but lower; all I know is PR209 works for me and PV19
doesn't, although my favorite is PR175, a VERY eccentric (as far as
being way off from process magenta) pigment that I wouldn't recommend
to anyone.

And while this discussion is more about the magenta than about the cyan,
while I'm at it I'll say that it looks like pthalo cyan (PB17) might be
a better match for a cyan process color than the pthalo blues, but only
one manufacturer uses it, and for my money, pthalo blue works fine.

The fact that people have been able to print tricolor gum with
reasonably good color balance using various pigments that don't match
the reflectance curves for process colors either shows tremendous luck,
or that there is much more margin for error than some might suppose.

Kees is right, it's unfortunate that two different colors are named
PV19, and that you have to be aware that there's a gamma and beta. The
pthalos are the same in a way; there are subnumbers for the phtalo 15's;
15:3 is greenish blue while 15:1 and 15:6 are reddish or middish blue.

(2) With all due respect to Bill Leigh, we're talking about color
photography and pigments here, not computer printers and inks or
commercial printing presses and inks, which have requirements and
problems and characteristics that have nothing to do with what we're
talking about. One of the sources of confusion that sometimes arise here
is when people get gum printing confused with commercial printing. They
have very little in common, as far as I'm concerned. And yes, in my gum
printing world, as in the world of other photographic tricolor
processes, three saturated primaries do produce a solid black.

Katharine Thayer
Received on Sat Jul 3 14:24:28 2004