From: Judy Seigel (jseigel@panix.com)
Date: 11/10/01-02:41:05 PM Z
Well, Sandy...
On Fri, 9 Nov 2001, Sandy King wrote:
> e. gum printers are by nature incapable of carrying out
> meaningful sensitometric testing,
I am not "by nature" a gum printer. Having arrived at this state through
other avenues (including landlady and paste-up-and-mechanical worker), I
claim many attributes... unless you think gum printing is so
virulent/powerful it wipes out the past ?
Tho this gum printer was focussed enough to disprove 50 years of canonic
myth in her first summer of serious testing -- Of course Anderson,
Crawford, Scopick & Dudley & Henney et al were ripe for the plucking, but
it was done with the 21-step, NOT "sensitometry." What was *meaningful*
was seeing through false assumptions (tho granted that took a while).
I doubt I'd base such a statement anyway on *sensitometric testing,* which
would be approaching a hair with a hammer. No matter the effects of gum,
I'm still quite able to count: I counted the steps on a 21-step, the new
am di had more of them. I can't SWEAR that the d-max was identical for
both, as the vicissitudes of hand coating (as Dave so eloquently notes)
could affect that, but in any event I've always found that the number of
steps is the safest guide to "speed."
As for accuracy in measuring ... Will try to dig the tests out from their
overgrown file, but I think my measuring is close enough for the purposes:
Paint is weighed by gram scale, liquid is measured by dropper, that is, by
counting drops.
> First, there has been at least one thread (and I think more) on the
> subject of the stability of dichromates, both in solution and in
> distilled water, with comments from persons with a lot of knowledge
That thread I don't remember, but anyway, I don't give a fig for
"knowledge of chemistry" -- because that's the part where they EXTRAPOLATE
from some other test, without having replicated the conditions at issue.
In fact it occurs to me now that some of my findings were possible due to
my lack of "knowledge of chemistry."
> of chemistry. As I recall the bottom line was that this chemical is
> highly stable in both powder form and when mixed with distilled water.
I don't recall that bottom line. Where is it? Even so, see my remarks
above about extrapolations. I kept the am di powder for 18 years (just
used the last of the jar, didn't try to check it against the first
formulas mixed with it, tho it looked the same). But "stable" is
relative, and strength of solution is an issue also. My mixed solution is
26%, the powder is 100%. And although some chemicals probably keep as well
in solution, experience says not all do.
> Second, I keep on hand numerous bottles of both ammonium and
> potassium dichromate in various strength solutions, all mixed with
> distilled water. Some of the bottles are several years old but I know
> from extensive testing that solutions several years old give
> identical speed and contrast in carbon printing to ones mixed two
> weeks ago or yesterday. I do a great deal of testing of materials and
> you can take that information to the bank and get a healthy return on
> it. I would add that I keep all of my solutions topped off, or almost
> so, in storage.
Hmmmmmm..... I had suggested that the mostly empty bottle could be a
factor in the deterioration, but you raise a point here -- if you keep
your solutions "topped off" in storage, then they're not aging, because
you add fresh. Then your finding wouldn't apply to dichromate stability in
SOLUTION. And since yours are not kept in partially empty jars our
comparisons are of different things in this as well.
So we have a couple of different questions:
1. How am di in solution would keep in full bottle.
2. If there's a difference in the way it does or doesn't keep in nearly
empty bottle.
And what else could account for difference in our findings. One point
again may be Dave's suggestion about the difference in MECHANICS of our
two processes. Another thought is difference in our concentration. As I
recall you're using a 2% solution -- might as well just say the words
"ammonium dichromate" in the room. Probably not nearly so strongly at
work, in the same way a puff of smoke doesn't affect one so much as a
roomful.
> Third, because of the small quantities of solutions (with the
> possible percentage of error) that are used in mixing gum emulsions
> for gum printing, I suspect that it is difficult, if not impossible,
> to carry out any meaningful sensitometric testing that would give you
> results with an accuracy of greater than 25%.
Again, I don't consider *counting* to be sensitometric testing. However
let the record show that SO FAR, when I have done sensitometric testing
it's been fine.
> So said, one of us probably deserves the "Often Wrong But Never In
> Doubt" prize on this one. Fit your hear or mine better?
Well, I'm still of the school that believes in cause & effect. I haven't
YET found results of any of my own tests "wrong," tho this could be the
time. Where I have been wrong has been in not understanding the vast swamp
of variables, as at first when I tested "gum printing" without realizing
gums vary, as do pigments, papers, and sizes. Not to mention weather and
wash water. However I like to THINK I cover my ass by saying "in my
experience." I have no reason as yet to think my finding on this point
was wrong, even if I were the only one to notice, which I'm not.
Not to mention that if I did err in the coating technique, as Dave
suggests, it would require a further coincidence -- that in BOTH the tests
I made, a while apart, the coat on the OLD am di just happened to be the
thicker one.
But I don't know how you would apply this coincidence to Katherine's
technique. She didn't speak of making 21-step tests, merely that the
solution was no longer usable. Since she was presumably printing, not
testing, she judged by something else, that wasn't "sensitometry."
Now I've used up the old am di powder, and plan to switch to k di, since I
have a jar of it on hand. I also have some old mixed k di on the shelf (I
think). So I'll compare that to the new one. In fact I'll go further, I'll
fill one bottle with k di solution and another with my usual 200 cc and
work off that... and check in let's say a year, as it lowers... should we
all happen to still be here and alive and care.
Judy
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