Joe,
Interesting results.
You are using a relatively high blue pigment concentration and therefore
you get few steps and more staining IMHO.
I use far less pigment but even so get some stain, as you can see in
this strip:
http://usuarios.arsystel.com/tksobota/WN_Phthalo_blue_strip.jpg
The pigment is Winsor & Newton Winsor Blue (Copper phthalocyanine PB15)
0.15g in 10cc gum + 10cc saturated Amm. dichromate.
As to the blacks, that is still a mystery, I have not been able to find the
posts that Christine mentioned. I have looked in Jun2004 to Aug2004.
What I found is a post by Judy (I think) extolling the virtues of Kremer
lampblack. I found a few art dealers here in Spain that carry Kremer pigments,
so I will try.
Wow, wet plate collodion is fascinating. Some day I'll have to give it a try.
I already have the Scully & Osterman guide and some more material, now
I only need time...
Tom
At 21:55 05/12/2005, you wrote:
>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 Wed Dec 7 07:49:40 2005
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