U of S | Mailing List Archive | alt-photo-process-l | Re: Gum calibration (was: Paper negatives- Ink Selection)

Re: Gum calibration (was: Paper negatives- Ink Selection)

Keith, on that point I defer to Mark; I was just pointing to his
comment which seemed to support the idea that these variables aren't
likely to have a big effect on exposure time. All I can attest to,
myself, is my own experience with a great lot of different kinds of
negatives over two decades. With negatives made of prints
photocopied onto transparencies, silver film and paper (analog)
negatives, negatives printed on laser printers of various
resolutions and inkjet printers of various generations on various
paper and transparency media, negatives carefully colorized and
calibrated to the proper DR and curves generated to match the
emulsions and printing protocol, both greyscale and colorized ...
with all these different kinds of negatives my exposure times have
remained constant except for variations directly related to changes
in humidity, pigment concentration and other such printing-related
variables. As a result of those years of observation, I have arrived
at the (tentative) conclusion that while there are many variables
that affect exposure time, negative variables are not a significant
factor. I would be happy to be proved wrong by data, but theoretical
arguments in the absence of practical dat aren't terribly persuasive
to me.

I understand what Loris is saying, I think, that theoretically one
should expose longer in order to print the highlights if the DR of
the negative is too high, so it follows to reason that if you're
printing with the right DR negative the exposure time "should" be
shorter, but in practice it doesn't really work that way in gum, at
least in my experience; if you expose long enough to expose the
highlights of a negative that's too dense for the process, you're
going to expose so long that you'll block up the shadows, and you're
just going to be robbing Peter to pay Paul during the development:
if you develop long enough to open the blocked up shadows, you may
well lose the highlights in development anyway. So I think in
practice most people just settle for multiply printing those
negatives to get the highlights and shadows in separate steps. But
that's what works best for gum printing anyway, if you want to print
a longer print tonal scale than say a log density range of around .
75, which is about the most gum will print in one coat; since you'll
get smoother tonal gradations in the highlights using a lighter
pigment mix, and of course darker DMax in the shadows using a heavier
pigment mix. If you really want to print a nice long print tonal
scale with nice gradations throughout the scale, this double printing
is the only sensible way to do it IME.

As I said, I'll be glad to be convinced by actual data, but I'm
certainly not persuaded by the theoretical argument that since Loris
and Keith do everything the same except how they produce the
negative, then the difference in their exposure times must be
because Keith isn't doing his negatives right. There are just too
many things that could be different enough to account for the
difference, without bringing the negatives into it, and I am just
really philosophically opposed to any suggestion that anyone is doing
something "wrong" in their gum practice; I will always resist that
kind of characterization of one gum printer by another. But I've
made the point and will stand by for actual data to the contrary.

I think people read too much into what I say sometimes; I'm certainly
not against calibrating and developing curves for negatives. All I'm
saying is that if you're doing it with the goal of reducing your
exposure times, my experience suggests you will be disappointed.

At any rate, if you want a really good calibration system, the best
system in my opinion is to follow Michael Koch-Schulte's tutorials
using his RNP arrays to determine the color and Chart Throb to
determine the curves. I don't recommend doing it the way I did,
spending months going over and over and over things and calibrating
dozens of pigment colors at many different concentrations, until I
understood all the ins and outs of what was going on, but that's just
how I am; I have to understand things. You can actually get to a
very quick and reliable result just by following the directions.



On Oct 18, 2008, at 12:39 PM, Keith Gerling wrote:

Sorry Katherine (and Mark), but it doesn't make sense to me why ink
would not be a factor. Certainly inks are different. And certainly
the amount of ink the printer discharges can vary, or there wouldn't
be so many paper profiles. We are talking ink on paper where before
this group used to talk about silver on film base. Certainly the
amount of silver is a major factor when printing with traditional


On Fri, Oct 17, 2008 at 7:25 PM, Katharine Thayer
<kthayer@pacifier.com> wrote:

Keith, I've said this before, but since it keeps coming up I'll
say it one
more time: if your goal is to reduce exposure times, this isn't
the most
fruitful place to look IMO.

Mark has pointed out that exposure time isn't a function of
printer, ink
type, ink color or printer settings:

ender100 wrote:

Exposure time does not depend on the printer, ink or color of the
negative—it merely depends on the substrate you are printing
on—providing all other variables are equal.

and logic says that exposure time can't be a function of curves,
since the
exposure time is established before the curve is calibrated, and
change after the curve is calibrated. Exposure time is a function
of a lot
of things such as light source, dichromate concentration, pigment
concentration, paper speed, environmental conditions; how the
negative is
generated is not a significant factor, in my experience.


On Oct 17, 2008, at 12:00 PM, Keith Gerling wrote:

It helps. The negatives are pretty dense. When you started to talk
about negative density I was getting concerned. The only Pictorico
negatives I've actually held in my hand were some made by Sandy King
and I was astonished that he was able to get such a range of tones
from something that looked so "thin". Your paper negs don't look
different from mine.

2008/10/17 Loris Medici <mail@loris.medici.name>:

17 Ekim 2008, Cuma, 5:50 pm tarihinde, Keith Gerling yazmış:


I'd be very interested in seeing
a snapshot of one of your un-oiled negs, if that would be
Just something that give me an idea of your range of tones.

See here:

1. http://tinyurl.com/68txaw
(full 400dpi scan downsized to screen resolution)

2. http://tinyurl.com/698az2
(100% crop of the 400dpi scan)

Hope that helps somehow...