Hi Mark,
Thanks for your response, I wrote my last two before seeing this.
Yes, pigment and dichromate are the main variables that affect
contrast, although there is some evidence that the light source and
even the gum brand may be implicated.
Katharine
On May 4, 2006, at 9:47 AM, Ender100@aol.com wrote:
> Hi Katherine,
>
> Thanks for your response, I understand now what you were saying
> regarding the tonalities with gum—that's what I thought you meant
> originally, but my thick brain intervened.
>
> It would seem then that to get the "best" one print gum, then one
> would have to play with some variables, and you gummists have
> probably already done this.
>
> Starting with the best paper/sizing combination which prints
> smoothly with longest tonal scale, adjust the following variables
> until you get the longest scale on a stouffers, the highest Dmax,
> and smoothest tones. Obviously there would be tradeoffs.
>
> 1. Adjust amount of dichromate higher for longer tonal scale until
> no gain is seen.
> 2. adjust amount of pigment higher for greater dmax until tonal
> scale begins to fail.
>
> Other variables you could tweak?
>
>
> In a message dated 5/4/06 10:31:00 AM, kthayer@pacifier.com writes:
>
>
>> 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=
>
>
>
>
>
>
> Best Wishes,
> Mark Nelson
> Precision Digital Negatives--The Book
> PDNPrint Forum at Yahoo Groups
> www.MarkINelsonPhoto.com
>
>
Received on 05/04/06-11:36:02 AM Z
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