From: Christina Z. Anderson (zphoto@montana.net)
Date: 06/29/03-07:09:20 PM Z
Hi Joe,
I think I didn't explain clearly so here goes--what I did was do three
test strips of JUST dichromates (no pigment or gum): am pot and sod. I
exposed them at exactly the same time. I got a print of the step wedges
(dark numbers) on all three. I developed in water as per normal. I dried.
I observed. And then I cleared in pot metabi and observed. Before the pot
metabi clear I had three printed step wedges with more steps printed and
more contrast exhibited in the am di wedge. When cleared, all three cleared
to paper base white except for the overexposed borders on the prints which
were the usual green chromium stain(not the yellow) that won't clear with
pot metabi. The numbers and steps all disappeared with a clear in pot
metabi.
My observation was that am di was faster--it exhibited more steps.
Katharine corrected me in that it was chromium stain that was being
exhibited, because without gum there is no gum hardening happening. I still
assumed, though, that the greater amount of steps indicated faster exposure
in am di, so I retested with pigment and gum added, and the same results
occurred--I got more steps out of am di 30% than pot di 10% or sod di 100%
saturated solutions.
Sodium dichromate is thick, syrupy, super saturated, and not too much
faster in speed than pot di. Both are slower than am di, at saturated
solutions. I have now tested with 3 different tests and now different times
(1mn, 3mn, 5mn, 10mn) and it is consistent.
What I don't know and maybe you can answer is this: do two steps on
the 21 step wedge equate to a stop? If so I would say am di is faster by
about a stop to a stop and a half.
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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