Re: son of a gum tonal inversion test

Greetings from Wyoming,

Joe, thanks for the link to your test strips. A great illustration of
staining from too much pigment.

I'm using powder pigment Copper Phthalocyanine (Winsor Newton's Winsor Blue)
at 1g per 130ml gum. The gum/pigment is usually mixed 1:1 with either
ammonium or potassium dichromate solution. It produces a strong print with
no staining in the highlights. I did use the hotly debated "pigment dot
test" to help arrive at that optimum ratio.

Phthalo blue is a great color. Cheap, readily available, fantastic covering
power and beautiful. When I lived in New Jersey, I researched sources for
phthalo blue powder pigment. It's widely used and I did find wholesale
sources for 55 gallon drums of the stuff! Yeah, that's overkill. I'm still
using my little bottles of Winsor Newton Winsor Blue. A little bit goes a
long way.

I've also seen the strange tonal reversal that you've experienced with
Daniel Smith's Bone Black. I've experienced it using Sennelier's Mars Black
and Black For Fresco (powder pigments) used at higher concentrations that
cause background paper staining. It seems that minimal exposure (as seen on
the higher points of the step wedge) will help clear certain pigments off
the paper while non exposed areas are heavily stained. No idea what's
causing it, but the effect disappears at lower, non-staining pigment
concentrations.

Best regards,
Dave Rose

----- Original Message -----
From: "Joe Smigiel" <jsmigiel@kvcc.edu>
To: "Joe Smigiel" <JSMIGIEL@kvcc.edu>; <alt-photo-process-l@sask.usask.ca>
Sent: Tuesday, December 06, 2005 5:18 PM
Subject: Re: son of a gum tonal inversion test

> Perhaps the third time is a charm. Looks like the message I sent Monday
> and earlier today didn't make it through to the list. Apologies if you
> get a duplicate (or triplicate). The original message:
>
> OK gang, here's a couple more scans from yet even more gum tests.
>
> First is a test using a pthalocyanine blue (Daniel 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
Received on Wed Dec 7 21:47:16 2005