Re: Tonal inversion (was (Gum) Tonal scale)

Tom,

In actual practice I would attempt using a much lower concentration of
phthalo blue pigment. I just started with the 1gm pigment: 15ml
sensitized gum ratio to keep things constant between the initial tests
of this pigment and others like the cobalt violet or black pigments. I
did this specifically to show that pigment concentration has to be taken
into account for each specific pigment if any useful measurement of
exposure scale for that pigment mix is to result.

I think it also illustrates the potential for some pigments to stain
readily while others do not, and also that the same concentration of
specific pigments may result in underexposure or shifting of the
resultant tonal scale of the print, flaking of the emulsion with certain
pigments, the difference between maximum reflective density and tonal
scale, etc.

I'm impressed with the lack of staining in your phthalo blue example.
Can you also please share information on the paper used, how it was
treated (sized in?, hardened in?), etc.?

Thanks,

Joe
___

>>> tsobota@teleline.es 12/07/05 8:48 AM >>>
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 08:56:46 2005