From: Christina Z. Anderson (zphoto@montana.net)
Date: 06/30/03-08:54:17 AM Z
Sandy,
Thanks for the info below--I haven't step wedged since I started
photography (I've always said I am not a scientist!) I had to dig mine out
of storage (and then ordered 2 more--but no directions!).
Forgive me if, below, I ask silly questions, but I have to clarify this
all in my head; I feel like the proverbial (blonde?) woman going into a car
mechanic garage saying, "My motor is making this weird ping ping noise..."
With what you are saying, then the first step where I no longer see
the black number in the black square, and when there is not a definable step
between two numbered squares, would equate to maximum black--maximum red, or
blue, or pink, or green in this case, correct? If that is true, then my
results still stand that the am di reaches this sooner. I find the maximum
black happens sooner (toward white, higher number) on the am di than the sod
or pot. How I was (erroneously) reading the "speed" was that if the number
of steps went further down on the scale toward the 21, then the solution was
faster.
Now, to contrast: you're right, I must be confusing contrast and speed,
in the gum process. If I see no steps printed, let's say, from numbers 12
to 21, I am assuming it is that no exposure occurred and it is a speed
issue. You are saying it is a contrast issue? I can understand that in BW
photography (printing with a 1 filter vs. a 5 filter where no exposure
occurs in the highlights) but if the am di prints sharp, clearly defined,
and more steps, is it at all safe to say it is faster and lower contrast?
Or does the number of steps ONLY equate to contrast?
One thing I haven't done, which you say below, is compare the three at
non-saturated solutions, or take all three at, let's say, 7% so that I can
be sure to be below the pot di's saturation point. Do you think that that
test would be more valid to do than the one I am doing now (using all at
their saturation point)?
As always, I am mostly interested in practicality. My bottom line is
ease: so it is easier to dump the dichromate in distilled water and fill it
up so that there is always sediment in the bottom, to assure a saturated
solution. So my reasoning for testing the three side by side *and * at
saturation was to see for myself if am di is such a problem, as some say,
with staining and low contrast, and if sod di had any benefits
whatever--assuming at 100% saturation it would have the benefit of speed.
It seems from all the literature that the pot di is the most commonly
used form. I always use am di because I learned on it. I personally find
that the fact it is so quick to expose and prints more steps, or midtones or
whatever the terminology is, makes it my first choice to reach for in gum
printing. Then pot di, as Dave Rose says, for the final coat. Sodium--I
still can't see why to use it, except as Judy says that you could almost
infinitely dilute it, and it would be realllly slow. But it seems to me you
could handle that with timing under the UV.
Sorry so wordy--so much easier will it be to do this in person.
Chris
> However, I think you are confusing speed and contrast. The speed of a
> photographic emulsion is generally considered to be the point on the
> step wedge where you have the first maximum density in the shadows.
> Contrast is determined by how many visible steps you have. Less means
> a printing exposure scale of greater contrast, more means less
> contrast.
>
> In your tests what you have found is that ammonium dichromate gives
> less contrast, or softer results, than the other dichromate. This is
> true even when the dichromates are compared at the same strength
> solution.
>
> Sandy King
>
>
>
>
>
> > It's kind of worthless information, actually, but it was done in an
> >effort to see if for any reason I would keep sodium dichromate on hand,
> >assuming that the 100% saturation would be of benefit. I do think there
are
> >benefits to having pot and am both, but cannot see why I would ever use
> >sodium di again (unless it is really cheap? Can't remember).
> >Chris
> > ----- Original Message -----
> >From: "Joe Smigiel" <jsmigiel@kvcc.edu>
> >To: <kthayer@pacifier.com>; <alt-photo-process-l@sask.usask.ca>
> >Sent: Sunday, June 29, 2003 6:20 PM
> >Subject: Re: lemon juice and gum printing
> >
> >
> >> Chris & Katherine,
> >>
> >> I think what is being demonstrated here may be underexposure (or
speed) of
> >the Na & K flavors rather than any dichromate stain. The fact that
numbers
> >and letters remain with the ammonium exposure indicates that a chromium
> >image, not a non-image stain, has resulted using that salt. A "stain"
IMO
> >would be a general overall fog and not an image as you describe here.
The
> >step wedge has blocked exposure in the dense areas (numbers) and formed a
> >reversed image of them if I'm reading this correctly. That's an image.
> >>
> >> Also, I'm not sure what you mean when you say you cleared the print.
Was
> >this plain water or something like potassium metabisulphite? Water would
> >leave the image/stain intact (assuming sufficient exposure) while the
latter
> >would wipe out any chromium image or stain.
> >>
> >> Joe
> >>
> >> >>> kthayer@pacifier.com 06/29/03 11:30 AM >>>
> >> > Hi Keith,
> >> > One thing I did today, too was to do side by side exposures of
am,
> >> > pot
> >> > and sod di to see if there was a speed dif. I swear, am di is
really
> >> > fast! It gives the clearest, sharpest steps of all three
dichromates, is
> >> > the speediest, and sod is not much different than pot. I did this
test
> >> > with NO pigment, just side by side straight dichromate. Then I
cleared
> >> > to see what remained, and the am di was the only one that printed
the
> >> > numbers and the words and the steps of the tablet.
> >>
> >> Hi Chris and all,
> >> I think what you're demonstrating here isn't how the three dichromates
> >> print in normal gum printing so much as you're providing support for
the
> >> idea that ammonium dichromate "stains" (meaning dichromate staining,
not
> >> pigment staining) more than the other dichromates, which I haven't
> >> observed myself but others have reported. If there's no pigment in the
> >> coating and you still see the numbers, words, and steps of the tablet
> >> after the print has been cleared, then you've got dichromate stain,
which
> >> in my experience generally results from overexposure.It may be that
people
> >> want to print with dichromate stain rather than with pigment, as in
your
> >> historical example, but we should be clear that that's something
different
> >> from the usual printing practice.
> >> kt
> >>
> >>
> >>
>
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