Re: Gum tonal range (was Miracle size for gum)
P.S. I should probably add that when I did that demonstration, my
purpose wasn't to see how long a tonal scale I could print, it was
simply to show how print density is related to pigment concentration.
On Oct 12, 2009, at 8:37 PM, Katharine Thayer wrote:
Odd, I didn't get phritz's post, just etienne's response.
Yes, I'm talking about the tonal range of one printing.
Understand, I'm not giving "the print tonal range of gum" as .75,
it's just that those three pigment concentrations of iron oxide
black printed an identical range of .75; the range just moved
down the scale as the pigment concentration increased. But I'd
have to do a whole lot more testing than I have any interest in
doing, to make any general statement about the tonal range of gum.
This pigment (PBk11) is a weak pigment and requires a lot of
pigment to reach a particular color depth, so even the medium-dark
concentrations have quite a lot of pigment in them., and the
darkest one has a whole tube of paint dumped into about 15 ml gum,
as I recall. It would probably be easier to get a longer scale
with a carbon black that has a lot more pigment strength.
Marek's examples are the best tonal range I think I've seen in
gum. I tried the bleach development and couldn't make it work
for me; I've forgotten the details now, but he's definitely got it.
On reflection while cutting and hauling brush today, I'm not sure
I'm entirely in agreement that the transfer function for gum is
nonlinear, but I'm too tired to put my mind to it tonight. I do
agree that it works better to work from a long-scale negative and
print the various parts of the range separately, rather than to
print with a shorter DR negative; this goes back to a discussion a
few weeks ago. A light pigment load of almost any pigment will
print heavenly subtle smooth gradations in highlights much like
palladium, as long as the tones are there in the negative to print.
On Oct 12, 2009, at 4:51 PM, etienne garbaux wrote:
i've been wondering, is this discussion about exclusively about
one-layer-gums? i think it is.
I'll let Katharine speak for herself, but it seemed clear that she
was referring to a single layer -- did you look at the link she
provided? She clearly said in a previous post that to get smooth
tones and wide DR, you need to make multi-layer prints.
* * *
katharine, with your .75 density range, did you mean single layer
or finished print?
the other thing is, that all tonal ranges are a continuum between
black and white. there aren't any steps in reality. even in an
extremely short tonal scale is every single shade of grey present
in it. it's just a matter of a suitable negative to print them.
True, but.... It is all a matter of mapping. Mapping luminance
values in the scene to density values in the negative that will
enable you to further map them to the desired reflection densities
in the print. This discussion has focused on the second half of
that mapping, the transfer characteristic of the printing process
-- how the various densities in the negative map to reflection
densities in the final print.
If one is trying to get "every single shade of grey" in the final
print, there are easier ways and harder ways. (As a side note,
even printers who do not intend to use all the shades of grey in
any of their images are probably well served by learning how to do
so, just as singers who never intend to pop up and down an octave
at a time in performance nevertheless are wise to do so when
practicing.) Any high-contrast printing process makes getting
smooth transitions and all shades of grey in the final print
difficult. It's much easier to differentiate the tones in the
scene clearly when you expose and develop the negative (i.e., make
long-scale negatives -- as long as you don't run out of the film's
capacity to render them), then use a low-contrast printing process
to map the well-differentiated values in the negative to the final
print values. (The same applies, mutatis mutandis, to digital
imaging, as well.) Asking a printing process to amplify
gradations -- to dig them out of a negative when they are barely
there in the first place -- is rowing against the current.
Of course, gum printers come from this the other way round --
faced with a process that is inherently quite contrasty and
nonlinear, how does one get the tonal range one desires? Multi-
layer printing is one of the most powerful tools, as I understand it.