Re: Gum tonal range (was Miracle size for gum)
Etienne, thanks for reply. I accept the quibble over the exactness
of "literal" processes; I didn't intend to imply that I think that
the equation holds *exactly* for those processes, or for those
processes from the negative to the print. I was just trying to make
the point that while the equation holds (even if only approximately)
for those processes, it doesn't apply at all to gum, and to argue
against the suggestion, made at times in this thread, that a certain
number of steps or "stops" should, using that equation, translate to
a given print density range by multiplying the steps by .15 or the
stops by .3. It just doesn't work that way, is basically all I was
saying, and I think we agree on that.
And I agree, BTW, that many very beautiful photographs have a narrow
tonality range (I think of Joyce Tennyson's very high key images or
Bill Jacobsen's very low-key portraits).
Certainly most expert gum printers do have a repeatable process that
is quantified (or intuitively codified) within their own practice,
and if anyone thought my remarks were an argument against having a
repeatable process, they haven't understood anything I've said for
the last 12 years on the list. It's just that using the equation
from other processes is not the way to get there, as it is
meaningless for gum.
Not sure why you thought your last paragraph would antagonize gum
printers; I agree with it completely. I've always said that in any
one gum printing you can have either drama or subtlety, but not
both; my recommendation on my page on gum and tonality is that if
you want your print to have a longer tonal range with subtle
gradations throughout the range, the only way to do it, really, is
by multiple printings. Gum printers understood that a hundred years
ago, and it's still true. Again, thanks for dialogue.
Katharine
On Oct 11, 2009, at 3:37 PM, etienne garbaux wrote:
Katharine wrote:
Goodness, this thread has been confusing.
Amen. Discussions of "stops" always are, because so many people
fail to observe the distinction between the *exposure scale* of a
printing process and the *density scale* of the resulting print.
And you are right, the "more literal" processes (silver, carbon,
and PT for sure, and some of the other iron processes) obey a
substantially law-like behavior that tempts folks to make this lazy
and incorrect gloss. But even with respect to these processes, I
believe it is a dangerous conflation (see below).
The same sloppiness affects most proponents of the Zone system, who
forget that zones are print densities and often talk of the "zones"
of a scene that hasn't been photographed. The whole point of all
of the sensitometry/densitometry is that we have significant
control we can use to map the various luminance values in the scene
to print values (densities) of our choosing. IMO, this is properly
done by, first, deciding how much density range one wants in the
final print, then working backwards toward the range of important
scene luminance values. Not every print demands a reflection
density range from 0.01 log to 2.5 log (though it seems that many
zonies would die before showing a print that doesn't contain the
full range of reflection densities available with the chosen
process). Some incredibly beautiful and moving photographs have
reflection density ranges of less than 1.00 log placed everywhere
within the 2-or so log range of what I'm calling the "more literal"
processes.
However, note that the mapping from negatives to prints is rarely
1:1. That is, rarely does one stop (0.3 log) of increased exposure
produce one stop (0.3 log) of density increase in the print. Thus,
I must disagree to this extent with Katharine's statement:
But that relationship, that holds for how the silver was deposited
on the film strip, does *not* hold for the printing of the gum
through the test strip, and does *not* mean that for every step of
gum printed, there is .15 more optical density in the print.
With this niggle, I generally agree wholeheartedly with Katharine's
points.
the equation that relates exposure to density of reaction product
to optical density of tonal values *does not hold for gum,* and it
makes no sense whatever to talk about tonal range in gum, or even
steps printed in gum, in terms of stops of exposure.
* * *
With gum, the print tonal range is more a function of pigment and
pigment concentration than of negatives or exposure. The maximum
and minimum absolute densities are determined by the pigment and
the concentration of that pigment in the emulsion.
Not being a gum printer, I cannot say from experience, but one
would hope that the more methodical gum workers would get at least
an approximation of repeatable results if they used the same
pigments and concentrations from one session to the next. Granted,
the specific mapping will be different from the mapping of what I
have called the "more literal" processes -- but then again, the
"more literal" processes are not monolythic in this regard. A high-
contrast silver-gelatin paper will produce a reflection DR of
around 2.0 log with an exposure scale of around 1.0 log, while pure
PT with no contrast agent, or salt paper, will produce a reflection
DR of 1.7 log or so with an exposure scale of as much as 3.0 log.
(Of course, everyone's mileage will vary.)
(Now, here's where I risk antagonizing partisans of gum. Honestly,
I'm not trying to.)
The real differences, it seems to me, are the low reflection DR of
gum prints and the substantially nonlinear mapping of exposure
scale to reflection densities that seem to be persistent
characteristics of gum. (Actually, it appears to me that it's a
bit more complicated than that. I have seen gum prints that
exhibit reflection density ranges that appear to me to be in excess
of 0.75 log, but in general to my observation, the greater the
reflection DR, the greater the contrast and the less smooth and
linear are the tonal transitions. A reflection DR of 0.75 seems to
be what is achievable by a careful worker trying to get smooth
tonal transitions. So, it appears to me that you can have a
greater reflection DR, or you can have smoother tonal transitions,
but you can't have both at the same time. But again, I am not a
gum printer.) I must confess that because of these
characteristics, many of the gum prints I see do not impress me
particularly. That said, some workers -- many of whom are on this
list -- have made absolutely stunning gum prints, and my hat is off
to everyone who has persevered with the medium until they can
achieve the results they are after. I believe gum may be the
hardest alt process to really master.
Best regards,
etienne
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