Gum tonal scale (Re: How to apply curves in PS for digital negatives...

From: Katharine Thayer ^lt;>
Date: 11/30/05-08:44:26 AM Z
Message-id: <>

On Nov 29, 2005, at 11:29 PM, wrote:

> If you match the density range of the digital negative to the
> exposure scale of the alt process before you build the curve, you have
> won half the battle.  Then the curve doesn't also have to adjust for a
> mismatch of exposure scale and density range. 

Ah, that perhaps answers my question. I was wondering, last night,
whether you *really* meant Exposure Scale to mean one specific number,
which would indicate "the" number of steps that a particular process
will print, and then decided I was too tired to deal with it, so I
didn't ask the question. This response above, using the definite
article ("the" number of steps that a particuar process will print")
seems to suggest that yes, you do mean that for any process, you
think that there is a number called "Exposure Scale" that can be
plugged into the curve-mapping algorithm; any curve for that process
will generate that many steps in the final print?

If this is so, and if you mean to include gum in the processes that can
be so neatly plugged into the algorithm, then I would have to
disagree; while the average number of steps is five or six, the number
of steps (Exposure Scale if you will) will vary widely, depending on
the dichromate concentration, the pigment chosen, the pigment
concentration, the skill of the printer, the aim of the printer for a
particular printing, the exposure/development balance, and so forth.
It seems to me that you would have to use a different exposure scale
and a different curve for every single printing, unless you used the
same pigment at the same concentration and held everything else
constant for every printing you ever did. For someone like me, who has
a different "look" in mind and takes a different approach to every
project I do, this wouldn't make any sense. I just prefer to use the
same ordinary negatives and vary the printing to get the different
looks I want, rather than developing a different curve for every
printing. But this is another example of the many different ways there
are to in gum printing to skin a cat.

And then there's the point I raised yesterday or the day before,
cautioning against confusing the number of steps with tonal range of
the print. In gum, the number of discernable steps has little to do
with tonal range. In silver (or platinum, I presume) you can relate the
exposure to the number of steps to density to the tonal range; they are
all related in a lawful way. In gum, none of these laws apply, as I was
trying to explain to Yves the other day (and will make another stab at
making this point more comprehensible this morning).

For example: Yellows, as someone pointed out recently, tend to give
steps that are closer together than darker colors do. The steps you
get with a light pigment mix and a high concentration of dichromate
are IME closer together (more subtle tonal gradations) than the steps
you get using a medium pigment concentration and/or a lower
concentration of dichromate. And so forth. So not only do the
different pigments occupy different parts of the tonal range, but if
you expressed the difference between the lightest and darkest tones
quantitatively, I believe the tonal range would often be different
even when the same number of steps are printed. But more about all that
in another post, later.

I said yesterday that there are two ways to approach the problem of a
mismatch between what the gum will print and the density range of the
negative: (1) reduce the density range of the negative, or (2) print
multiple exposures to increase the tonal scale of the gum. Again, I
don't think there's a right answer to this; each person will have a
personal preference. I personally haven't been very attracted by the
prints (reproductions, admittedly) that I've seen of one-coat gum
prints that have been made by the process you seem to be describing, of
smooshing all the tones in a longer-range negative into a curve to fit
the short printing range of gum, however you want to define or label
that range. To me (and again it could simply be an artifact of poor
reproduction, or the curve wasn't developed in as sophisticated a way
as you are doing, perhaps) these prints simply aren't very
interesting, and I personally prefer a gum print with more tonal
range and more depth to it. But, each to his own,
Received on Wed Nov 30 08:46:26 2005

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