From: Dave Rose (cactuscowboy@bresnan.net)
Date: 09/27/03-07:11:53 PM Z
I've actually done the "GPR test" many many times, using dozens of different
pigments. I FULLY UNDERSTAND ITS LIMITATIONS. (Judy are you
listening?)I've found it helpful as an easy and simple test for quickly
determining the relative strength or weakness of pigments.
Here's a good example of how the GPR test works. Take two dry pigments, W/N
Winsor Blue (phthalo) and Old Holland Burnt Sienna and perform the GPR test
per instructions in Crawford's The Keepers of Light. Results indicate that
phthalo blue has a far greater tendency to 'stain' (leave a visible dot)
than the Burnt Sienna. After further and more accurate testing using
sensitizer, and in actual practice (making gum prints), I use Winsor Blue at
a 1gram/130ml gum ratio and Burnt Sienna at a 1gram/12ml gum ratio. With
both pigments at these respective ratios, I can produce single exposure
prints that exhibit deep, rich shadows and clean, stain-free highlights.
The GPR test helped me determine the final ratios used more quickly, thus it
has value to me.
I had done extensive testing and made hundreds of gum prints many years
before Judy published Post-Factory Photography. Her articles on gum are
interesting, but IMO, they're limited in scope, and sometimes promote hasty,
erroneous conclusions based on insufficient testing and data. From
everything I've read in Post-Factory Photography and on this list, Judy has
never given the GPR test a fair shake. It seems that she's more interested
in discrediting and disproving prior authors on gum printing in order to
establish herself as the self-appointed 'new expert' on gum.
The text copied below is a prime example of how ridiculous the incessant and
pointless 'GPR test argument' has become. Can't we just agree to disagree?
I (and others) find the GPR test useful, despite its limitations. Give it a
rest Judy.
Best regards from Big Wonderful Wyoming,
Dave Rose
----- Original Message -----
From: "Judy Seigel" <jseigel@panix.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Friday, September 26, 2003 9:52 PM
Subject: the great GPR "test"
>
> On Fri, 19 Sep 2003, Katharine Thayer wrote:
> > I've never understood the virulence of the attacks lobbied here against
> > that pigment test and its proponents; it simply makes no sense to me. My
> > position on the pigment test, which I've elucidated at length before,
> > (anyone who's interested can consult the archives) is that if the test
> > is useful to you (as it was to me) use it and be glad for it, and if
> > it's not useful, don't use it. But to attack so vehemently those who
> > have used the test and found it useful, makes no sense. It makes no
> > sense in terms of community; it makes no sense in terms of science, it
> > simply makes no sense.
>
> > CUt ... (some say that the addition of dichromate DECREASES
> > the likelihood of staining; some (myself included) say that the addition
> > of dichromate doesn't seem to make enough difference to matter, and some
> > say that the addition of dichromate INCREASES the likelihood of
> > staining) the only possible thing that can be said about it, from a
> > scientific point of view, is that the evidence is inconclusive, and that
> > none of us can say with any certainty that we have the final answer on
> >
> > .... I just don't see any
> > evidence that supports the suggestion above that the pigment test should
> > be dead by now; the reason it's still around is probably that people
> > have found it useful.
>
> Sorry it took me so long to get back on this (reality again). I realize my
> words are probably futile, but for newcomers to the list, and what I feel
> is my debt to the sorry state of "science" in alt ("classics" I re-read on
> my "summer vacation" could plunge me into despair if I weren't so cheery
> by nature), I try again.
>
> Katharine has strangely re-written "history" above, which I cannot take
> lightly. Far from attacking "proponents, " I myself was nearly lynched on
> this list for heresy in doubting said GPR test -- mostly by Katharine
> herself, who found my disrespect for "authority" (Scopick) "disgraceful,"
> declaring "I hope I never see such a sight again," in about those words.
> Given the vehemence and emotion of her attack, I replied more mildly
> perhaps than I should have. If I'd made more fuss, revision might not have
> come so easily.
>
> Part of the problem seems to be trouble in distinguishing between
> disagreement with a theory and "attack" on a person, especially her
> person. I have certainly explained the nonsense of that "test," and may
> have to do so again, but if disproof/disagreement is taken as personal
> attack, we're all in trouble. (And reproaches about "community" are hardly
> more useful.)
>
> Now she says,
>
> "> ....some say that the addition of dichromate DECREASES
> the likelihood of staining; some (myself included) say that the addition
> of dichromate doesn't seem to make enough difference to matter, and some
> say that the addition of dichromate INCREASES the likelihood of
> staining) the only possible thing that can be said about it, from a
> scientific point of view, is that the evidence is inconclusive, and that
> none of us can say with any certainty that we have the final answer on
> this question."
>
> The only *possible* thing ??? Sorry, this is as *unscientific* a statement
> as I've read on this list. Scientific is not equivocations or assertions,
> it's controlled *tests*. Which I have done many times, and printed as
> evidence, and have yet to see or hear of any which contradict them. Even
> stranger, however, is that Katharine nevertheless proves my point !
> Actual gums, she allows, made with the dichromate and exposure, don't
> necessarily behave as predicted by the GPR test with just gum & pigment.
>
> Exactly. And, if you don't know the meaning of your "finding" (if it could
> mean more, less, or the same staining) until you've done the "real"
> process itself, what use is it? About as much as testing a car by kicking
> the tires. Adding the dichromate is no big deal, why go through a
> rigmarole that has to be checked against reality anyway?
>
> My own gum tests, as I have said repeatedly, exposed with the dichromate
> under a 21-step, never showed a "threshhold" past which stain occurred and
> below which it didn't -- as is the premise of the GPR test. If there's
> stain, more pigment may give more ABSOLUTE stain, but not more relative
> stain. I realize no "evidence" I produce (even should she read this far)
> can trump Katharine's conviction, but I refer others who may be interested
> to my extended explanations in the archive, also to P-F #2, p. 46, & P-F
> #3, p. 38, which shows a "solarizing" effect in stain in steps 10 thru 21,
> but steps 5 thru 9 with no stain at all. If this isn't evidence, what is?
>
> But, she asks, if the GPR test is not predictive, how come it's
> everywhere? How come 68% of the American public believe in angels with
> wings? Few persons putting that test in books (except probably Scopick)
> are likely to have done it, and none can have checked it against a
> control. It's most often performed by beginners (as Katharine was when she
> did it), who are unlikely to doubt holy writ of 65 years.
>
> Nor I expect does the beginner notice that the opening salvo in many of
> those GPR texts (including Anderson's original) is a gross error: "The
> longest scale of gradation is secured when the coating mixture contains
> the largest possible amount of pigment." More pigment may give more D-max,
> but also yield shorter scale because the shadows block up. This is hardly
> a recommendation for the rest of his act.
>
> Another popularizing factor is the placebo effect of the ritual. As an
> article in the latest Onion, "FDA Approves Prescription Placebo,"
> explains, "For years, scientists have been aware of the effectiveness of
> placebo in treating a surprisingly wide range of conditions" (although
> animal testing "for some reason was totally ineffective in determining its
> effectiveness"). However, the article concludes, "drug makers say placebo
> is safe."
>
> In gum printing, however, it is not safe. It's a false promise -- voodoo
> photography. Anderson's failure to understand the actual mechanism of gum
> (he seems to have done very few gums during only a brief period) may have
> contributed to his early abandonment of gum for oil printing.
>
> Finally, let us note that some of the earliest how-to articles on gum
> begin with an ode to how SIMPLE gum is. Demachy wrote that if he had to
> learn from some of the tracts that appeared later, he would have given up
> before starting. No recent book I know of would dare say gum is simple --
> the odes are rather to how difficult it is. That may be due to what in
> medicine is called "iatrogenic disease."
>
> cheers,
>
> Judy
>
>
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