From: Christina Z. Anderson (firstname.lastname@example.org)
Date: 07/14/03-12:52:29 PM Z
Rushing around as I am, getting ready to leave for APIS so I probably
won't do the testing until I get back, but:
Have to go get distilled water and run the test again at equal
saturations--both were used at saturation, and exposed the same time, so the
only thing the test shows me is that the sun will bleach out pot di--not
that it won't am di--at saturation levels commonly used in practice (10 and
30% respectively), and *reduced* chromium that is seriously overexposed in
the borders (whew!). I will mix up an equal proportion of each and see
whether this still holds true. Certainly in practice, as I had said, this
isn't very relevant because we use chemicals to remove stain very
effectively. I was actually just seeing if sun even HAD an effect on the
stain because it was...a weird thought. And I was surprised that lo and
behold it did?!
But get this, speaking of weird thoughts: I came across several times
in different authors, both current and past, that at a certain point, the
concentration of the dichromates does not increase speed!! In other words,
once past 5% it doesn't really matter much!!! Now, I have NO CLUE why some
people would say that or think that but it is yet another thing to test!
Because, if it is true, I'd save a lot of dichromate. I know Suzanne Izzo
uses her concentration less than saturation. Maybe at a certain point it
does its hardening thing and past that it doesn't matter. Please note I am
NOT saying this is true--but this, along with the bleaching of the sun on
dichromates, seems so bizarre to me and contrary to logical thinking and
what others say on this list if I remember, that I can't leave it alone as
a fallacy--aside from the fact that if it IS true, it would be of benefit.
Hence the testing. I think Sandy has probably done this type of test of
dichromates at different concentrations, or maybe you have, and can dispel
this heretofore myth (or confirm its truth!) and chime in here.
And, furthermore, Nadeau, as does Gassan and a few more people, points
out the fallacy that dichromates are not sensitive when wet, a fallacy as
Nadeau says has been continuing for 80 years. So there are lots of these
things floating around, as we all on this list know.
Back to the sun clearing:
1. The stain was in the borders of the print, not the image area.
2. At 5 minutes for each image the am di one wasn't massively
3. I actually always get pretty overexposed borders outside the image
area like that because I don't mask my negatives.
4. So in practice this does have an effect, and the effect on the
reduced chromium was perceptible through the pigment in the border areas,
too, that overlapped the sensitized paper parts. It wasn't just bare
5. My point was not that am di presents problems. On the contrary, I
much prefer am di because I'm used to it and how it performs, and pot di
frustrates me because it doesn't perform in the same way. But I don't
conclude from this that pot di is "no good" as it seems people will be quick
to say about am di.
Hope this answers some of the questions and the rest I'll address later
when I get back.
Bill, how did I miss you were in MT and where in MT?
----- Original Message -----
From: "Katharine Thayer" <email@example.com>
Sent: Monday, July 14, 2003 5:53 AM
Subject: Re: GUM TESTING
> Christina Z. Anderson wrote:
> > I think it may lead back to what Sil had said previously in the fact
> > remaining dichromate in the print after development in water wasn't
> > doing its "thing" and endangering the print if left in permanently---
> I think Sil was referring not to a visible stain (correct me if I'm
> wrong, Sil) but to what little residual chromium remains in a print
> that has no visible stain (the question, as I recall, was whether all
> prints should be cleared as a rule, as many experts recommend, even if
> there is no visible stain; for whatever it's worth, I agree with Sil
> that prints need only be cleared if visible stain is present) and was
> also referring, as I recall, to reduced chromium, not to hexavalent
> chromium. So I'm not so sure it relates. Since your post last night said
> that the old source specified that two hours in the sun would remove a
> YELLOW dichromate stain, I assumed you were talking about hexavalent
> chromium, which is yellow or yellow-orange, not reduced chromium, which
> is green or brown. It wasn't entirely clear from your description, but
> it sounds like maybe your tests were done not on hexavalent dichromate,
> but on reduced chromium. If we're going to do scientific testing, we
> need to be able to agree on basic terms and on what it is we're testing.
> > So you could actually just duplicate this with test strips exposed under
> > plain dichromate
> Actually, I couldn't, as long as it stays cloudy and showery; I may not
> get two hours of sun this week. But at any rate I'm still a bit puzzled
> about what it is exactly we're testing and how it relates to gum
> practice. The fact that your prints were exposed the same although the
> speeds of the dichromates are different at saturation concentration
> (which as I recall is the concentration you used) suggests that the
> residual chromium may be at a different stage in its reduction in the
> two prints to start with, which makes me wonder if your experiment is a
> valid test of whether the two dichromates really behave differently in
> this circumstance, as you concluded. If you started with each print
> exposed properly, meaning different exposures to allow for the different
> speeds of the dichromates, or used concentrations at which the speeds
> are similar, would the two dichromates behave more similarly as far as
> this question?
> But even more crucial to how this relates to normal gum printing: in
> order to get something to see using just dichromate, you'd have to WAY
> overexpose compared to how you'd expose for a normal gum print (To
> overstate the obvious for non-gum printers trying to follow this
> discussion: in normal gum printing, the image consists of hardened gum
> and pigment, not chromium; in a properly exposed print most of the
> dichromate doesn't change color and just washes away in the development;
> the only way to make a visible dichromate stain IME is to overexpose.)
> Maybe the overexposure overrides the speed difference; perhaps all the
> dichromate is completely reduced in both cases in your experiment,
> though it's hard to know. One thing that experience does suggest is that
> if the potassium dichromate was overexposed enough to darken the
> dichromate, then the ammonium dichromate at the same exposure would be
> done to a crisp.
> I am still curious and will run a couple tests when I can, but I may end
> up insisting on a different protocol for the tests that I run, because
> I'm not persuaded that your test provides adequate support for the
> conclusion you drew from it, quoting your post, "that if someone is used
> to pot bi (di) and makes a switch, am di "seems" to present problems."
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