son of a gum tonal inversion test

Looks like the message I sent Monday didn't make it through to the list.
 Apologies if you get a duplicate. The message:

OK gang, here's a couple more scans from yet even more gum tests.

First is a test using a pthalocyanine blue (Damiel Smith Thalo Blue) at
different concentrations of pigment. Starting dilution the same as I
posted the other day for other colors, namely 1 gram powdered pigment
per 10ml gum arabic solution and 5 ml saturated potassium dichromate.
Then cutting the pigment mix with additional gum and dichromate to get
ratios of 1gm:20ml:10ml, 1gm:40ml:20ml, and 1gm:80ml:40ml.

http://my.net-link.net/~jsmigiel/images/technical/gum/pthalo_test.jpg

This color printed out about 5 steps on average but all tests are very
heavily stained. This is typical for pthalo blues for me even though
others report printing it without staining. Again, the only time I've
ever printed a pthalo blue without appreciable pigment stain was usnig
Linel Hortensia Blue and even then there was a perceptible overall color
shift caused by very slight staining.

Now here's the interesting (to me) part. I also retested the Daniel
Smith Bone Black pigment that produced the tonal reversal the other day.
 For today's test I used the same pigment concentration as before, (1gm
powdered pigment in 10 ml gum + 5 ml saturated potassium dichromate), as
well as the same paper and exposure source. I reduced exposure from 600
to 75 exposure units based on the previous test to give me maximum
density at step #1 today. I based today's corrected exposure on last
week's intentionally overexposed print which first exhibited the tonal
reversal. (There's a little variation there probably due to mixing the
emulsion slightly different today, but the maximum printed density is
close to before.) I ran two tests with the same emulsion batch & paper
the difference being I intentionally coated both at the same time,
printed and processed one sheet immediately, and let the other sit in
the dark for an hour before exposing it. The latter print is just
barely darker and this difference could probably be equalized by letting
the print soak a bit longer. (Both were autodeveloped for 1 hour in 3
changes of water.)

The image linked below show last week's test adjacent to the two tests
run today:

http://my.net-link.net/~jsmigiel/images/technical/gum/black_reversal.jpg

Tom showed last week that the reversal shifts along the stepwedge scale
with exposure and I can confirm that observation today. (So, heating of
the emulsion under the most opaque areas of the light attenuator is
probably not the cause. It must be pigment and/or pH related.) As my
scan shows, the reversal effect still occurs even with reduced (and
probably optimal) exposure for this mixture. But, take a look at the
numbers! Not only has what should be the white field around the numbers
and the higher steps reversed, the numbers and letters have reversed as
well in the tests run today! The numbers should print as maximum
density yet they have printed as minimum density. Weird with a beard!

I'll let y'all discuss this amongst yourselves. I'm bailing. I'm off
to devote my time to wetplate collodion now.

Joe

>>> gauvreau-yves@sympatico.ca 12/03/05 1:53 PM >>>
Joe, et. al.,

Your absolutely right, in fact I would add that every things
(conditions,
variables, parameters or whatever) in play in a test like this will
influence the result in some way, may be it will be a very small
influence
not to say an insignificant one but it will.

Yves

PS. Many of you use from time to time acronyms I think there called,
like
here "IIRC" below. Would there be some place I could go to find out what
they mean if this exist???

----- Original Message -----
From: "Joe Smigiel" <jsmigiel@kvcc.edu>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Saturday, December 03, 2005 1:05 PM
Subject: Re: Tonal inversion (was (Gum) Tonal scale)

> Yves, et. al.,
>
> I just realized this effect is probably also related to specific
> pigments. (This would also support what Tom has observed IIRC, and
> perhaps also to Chris' observation regarding pH.) The reversal effect
> appeared when using bone black as the pigment but not cobalt violet.
> Each was given the same exposure which presumably would lead to
similar
> heating of the test wedge (assuming the integrator is working
correctly
> on the exposure unit). Since the bone black reversed and the cobalt
> violet didn't, something else must be contributing to or causing the
> effect.
>
> You are correct in that it may be very difficult to isolate the exact
> cause of the effect without introducing some other variable. I
> certainly don't have the means to do so.
>
> Still, it appears I have overexposed the bone black test by roughly
> 3.5-4 stops so I'll run a test at a much shorter and more normal
> exposure to see if the reversal effect dissappears at that level.
>
> Joe
> ---
>
> >>> gauvreau-yves@sympatico.ca 12/03/05 12:10 PM >>>
> Joe,
>
> This may well be the way to check this idea out but as you say it may
> introduce something else in the process. I think it would be somewhat
> complicated to verify this, with a high degree of certainty in
practice.
>
> In my own test, this happened to me as well and as soon as I reduce
> exposure
> a bit it didn't happen. This makes me believe that there could be
> somekind
> of threshold involved but again this is all very speculative on my
part.
> Maybe someday I'll have the time and the money to investigate crazy
idea
> like this one.
>
> Thanks
> Yves
>
>
> ----- Original Message -----
> From: "Joe Smigiel" <jsmigiel@kvcc.edu>
> To: <alt-photo-process-l@sask.usask.ca>
> Sent: Saturday, December 03, 2005 11:44 AM
> Subject: Re: Tonal inversion (was (Gum) Tonal scale)
>
>
> > >>> gauvreau-yves@sympatico.ca 12/03/05 11:06 AM >>>
> > >>... I think it could be caused by heat...<<
> >
> > I agree. This seems to be plausible explanation for the effect.
I'll
> > run a couple more tests reducing exposures or perhaps doing
> intermittent
> > ones to keep the negative (test wedge) from overheating and see if
> that
> > has any impact (although I might be introducing some sort of weird
> > intermittency effect by doing so).
> >
> > Joe
>
Received on Tue Dec 6 22:31:19 2005