On May 2, 2006, at 12:50 PM, Ender100@aol.com wrote:
> Katherine,
>
> I am not sure I understand your statement below. I understand that
> gum is a short scale process (requires a negative of a shorter
> exposure scale, like in the range of log .9 maybe to log 1.2, give
> or take a log or a twig—or from your example below, between log
> 1.5 and log 1.8?
>
> I also understand that no curve on a digital negative is going to
> change the exposure scale of a given mix, and certainly the curve
> is not going to INCREASE the printed gum DMax.
>
> What I am not sure I understand is if you are saying that for a
> given mix of gum printed with one coat, changing the shape of the
> curve will NOT allow you to get whatever tones you want between
> the DMax of this given mix (one printing) and paper white? And
> further that you can only obtain some of the tones ? Which ones?
>
> Let's assume that a digital negative can have a maximum of 256
> possible tones of density. (If that is ok with you) and that a
> radical curve is going will reduce the number of tones from 256,
> so let's consider a not so radical curve. Let's also assume
> that the negative matches the exposure scale of the gum mix before
> the curve is added.
Mark, I understand the theory here, but I also know gum, and I repeat
that I have yet to see a one-coat gum that prints tones from dark to
light, with all the tones in between. Maybe a better way of saying
that is that given the kind of pigment load that you need to get the
deepest DMax, the emulsion is going to be contrasty enough that there
will be gaps between the tones rather than a smooth gradation.
Surely you can see for yourself that Chris's gum print is jumpier in
tone than the platinum print; throughout the portion of the scale
that they both print, there are gradations of tone in the platinum
print that just aren't there in the gum print. So while it seems
theoretically to make sense to say that gum should print all the
little tones between the DMax and the DMin, the fact is that it
doesn't, not in one coat. Like I keep saying, I'm ready to be
pleasantly surprised, and this is what I'm aiming for with the back-
exposure experiments, but I have yet to see a one-coat gum that can
print a delicate gradation of tones throughout a full tonal scale.
Yes, of course, a one-coat gum can print a rather contrasty
approximation of a fully tonal scale, I would have thought that went
without saying, but like I say, there are "fully tonal" scales and
then there are fully tonal scales.
I do think Chris could get a better approximation to the smooth tonal
gradation of the platinum by using less pigment, but then the
question is whether you can get the DMax. Maybe, maybe not. And this
is the struggle always with gum, as Sandy and Terry and many others
have pointed out. More pigment means deeper DMax but more contrast,
less pigment means more subtle tonal gradation but less DMax. This is
the eternal equation of gum; it's got little to do with curves. Yes,
if you've got a really bad curve to start with, as Chris has here,
you can improve it, But you can't improve it beyond the limitations
of the particular emulsion you're using, which I suspect Chris may
have demonstrated in the prints she posted.
Katharine
Received on 05/04/06-09:28:32 AM Z
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