Re: Gum contrast - not that it hasn't been beaten to death

From: Katharine Thayer ^lt;[email protected]>
Date: 01/05/04-05:10:45 AM Z
Message-id: <>

Sam Wang wrote:
> While I was test printing gum on the Clearprint Vellum, it finally dawned on me, that the more
> smooth the paper, the higher contrast it gives in gum.

Sam and all,
I hate to always to be the contrarian,

(and before I go any further I might say something about contrariness):
I've been taken to task for often disagreeing with statements made here
about gum printing. I don't understand this criticism, as it seems to me
that the whole point of a forum is to debate issues. If it's rude to
offer differing observations, then what's the point of having a forum in
the first place? I don't think it would serve the cause of gum knowledge
to have the list be only a series of pronouncements, without any
discussion given to those pronouncements.

Anyway, as I was saying, I hate to always be the contrarian, but that's
not been my experience, that smoother papers give greater contrast.
Fabriano Uno, for example, prints with less contrast (for me) than many
papers that aren't as smooth. And while I can't claim to have much
experience printing on Clearprint vellum, the one test print I made on
it last summer, just to see if gum would print on it, had very little
contrast compared to the same image printed on Arches hot press, which
is not a very smooth paper in my book, especially since I always printed
on the back side which is subtly more like a cold press surface. (The
front side has a wire pattern that I found objectionable, so I liked the
back better.) The Arches image has mottling from some weirdness with the
internal sizing; that was one of the last prints I made on the paper
before abandoning it. There's also a potential confound from the
difference in negative types, although that confound is rendered fairly
null and void by the fact that I have printed the Pictorico negative on
similar papers (to the Arches) with a similar pigment concentration to
that used to make both prints shown here, and got the same ballpark
contrast as with the oiled paper negative I used here.

I found the image on vellum rather interesting, as it's another way to
get a ghostly effect that I've achieved before by a more difficult and
roundabout method, and intend to employ it in my work sometime. I should
add that I'm sure that if I wanted to monkey with it by changing the
curve of the negative or changing the pigment concentration, I could get
a more contrasty result if I wanted one; the purpose of this test
wasn't to see how well I could make gum print on vellum, but simply to
see if it would print at all. I should also specify that I used the
1000 weight; perhaps you're using the heavier vellum. I wouldn't say
that the vellum is particularly smooth; it has a pebbly surface that
shows less fine detail than, say, Fabriano Uno. I find the vellum
unacceptable for negatives (for my particular purposes) for the same
reason: the pebbling on the surface tends to blur the image.

The smoothest surface I've found for gum printing is Epson standard
inkjet paper, but it also prints rather flat and its (clay?) surface
hangs onto the dichromate, which has to be cleared later.

If I were to break my rule against setting down rules and attempt to set
down a rule about paper smoothness and contrast, my rule would be rather
opposite of Sam's, to wit: the smoother the paper, the more steps that
can be printed, because a rougher paper tends to obscure subtle tonal
differences. In fact, when I found myself a couple years ago wanting to
print ever subtler tonal gradations, I found that I could only get those
smooth and subtle gradations, such as in the skunk cabbage flower:

by printing on a much smoother paper than the back of Arches hot press.
But since I don't set down rules, understand that's not an actual rule
I'm setting down, it's just an observation, a surmise. It's possible
that the difference in observed contrast on the different papers might
arise from the different concentrations of dichromate that we use, in
other words, perhaps if you start with diluted dichromate you may find
that smoother papers print with greater contrast whereas if you start
with saturated dichromate you may find that smoother papers give less
contrast, but to determine whether that's so that would require
extensive testing that I'm not interested in doing. I also suspect
strongly that different light sources may interact with the contrast
variable in different ways, adding another level of complexity to the

 Maybe that's why those who sized their
> papers needed to lower the contrast of the emulsion by loading it with dichromate.

Nothing in my experience supports this speculation.
When I started out, I always sized my paper until one day when a gallery
wanted four tricolor prints right away and I didn't have any
sized paper ready to use. Just on impulse, I grabbed four pieces of
paper right out of the box, printed four tricolors, of which this was

and stopped sizing altogether from that day forward. I saw no
particular change in the contrast of my prints when I went from sizing
to not sizing.

There seems to be an underlying assumption in the phrase "needed to",
the assumption being that people wouldn't print with saturated
dichromate unless they were absolutely forced to by some "need"
otherwise they would print with less dichromate as a matter of course.
I've spoken to this assumption more than once, but will say again here
that I print with saturated dichromate for the simple reason that that's
what the instructions said that I used when I started printing, and I've
never seen any compelling reason to change. I can get every result I
want from the saturated dichromate; I like the printing times I get with
the saturated dichromate, and the one experiment I ran with diluted
dichromate was so objectionably contrasty that I'm not interested in
pursuing that line, although as I said at the time, I'm sure that one
could learn to print well with the diluted dichromate, given time and
practice and negatives optimized for the diluted dichromate rather than
for saturated dichromate. I'm just not interested in spending the time,
since I get everything I want with the saturated dichromate, and am not
convinced that the .625 grams of dichromate I use per four 8x10 prints
is a big deal to worry about. It's just that simple.

> So, that's another variable for the gum prpcess. With digital negatives that's of no concern though,

I don't understand why the purported contrast difference between rough
and smooth paper, in either direction, would not be a factor with
digital negatives. For the record, all the examples I have pointed to
above were printed with digital negatives of one type or another.

And by the way, when I ran that test a while back to check the
relationship between speed and concentration, I got intrigued with the
watery effect you can get by underexposing dilute dichromate, and have
been playing with this effect since. I've found that while oiled paper
negatives, which is what I used for the digital negative part of that
test since it's the type of digital negative I'm most familiar with (I
try not to muddy test results by introducing unnecessary variables, and
I've only used Pictorico for a few months) may give odd results, digital
negatives on transparencies give results that are much more consistent
with the results I got with a contone negative; in other words I'm
finding that I have to multiply the exposure times by four or five to
get an image at all, even a runny one, with the diluted dichromate.

Has the issue of gum and contrast been beaten to death? I doubt
it, since there still seem to be wide differences in observations that
bear on the question; if there was a consensus reached about gum and
contrast, other than the most general one that says that as a rule,
contrast varies as a function of concentration, I missed it.

Katharine Thayer
Received on Mon Jan 5 13:07:03 2004

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