From: Sandy King (sanking@clemson.edu)
Date: 02/26/03-11:25:27 AM Z
Cor,
In all of my comparison tests in rotary processing I have
consistently gotten a lower b+f stain with Pyrocat than with PMK.
Rollo Pyro (ABC+) gives about the same b+f as Pyrocat. In fact,
Pyrocat and Rollo Pyro give very similar results, but reading the
densities through a densitometer, even a color densitometer in blue
mode, can be misleading.
Here is what my observations and tests have revealed.
Rollo Pyro Pyrocat
Visual Reading .20-1.43 .20-1.40
Blue Reading .20-1.85 .20-1.70
Effective Density .20-2.05 .20-2.15
Range with UV
Printing
Essentially what I found, then, was that when staring with the same
DR in the visual, the Rollo Pyro (and PMK also) negatives show more
stain than Pyrocat-HD with a blue reading, but when printing with a
UV process the actual effective density range of the two negatives
was the same.
I have not tested VC and graded silver papers but given the fact that
silver papers have a lot of sensitivity to blue light I think it is
fair to assume that there would indeed be differences, as you suggest.
Recently I engaged in an exchange with Russell Welch as a result of
correspondence on one of the newsgroups and he verified that my
results by reading Rollo Pyro and Pyrocat stain with a UV
densitomete, XRite 361t to compare negatives from the two
developers; He used negatives that had been developed to an equal
maximum density as measured with a visual reading, that is R+G+B.
Visual D UV D
Rollo 1.27 1.90
Catechol 1.29 1.96
What his tests show is something that I have maintained from the time
that I first started working with Pyrocat-HD, that is, a reading
through a color densitometer does not give an accurate picture of how
the negative will print with a UV process, and that the the
yellow/brown stain produced by Pyrocat provides quite a bit more
actinic filtration than that of PMK and Rollo Pyro, which of course
makes perfect sense because yellow/brown is further removed on the
spectrum from UV light than yellow/green.
In principle this suggests to me that if folks are using PMK or Rollo
Pyro to make dual negatives, good for both silver and alternative
processes, they would actually get better results with Pyrocat-HD,
since with a same visual density range that could be used for silver
you would get a higher effective density range for UV processes. And
the difference between the blue reading of PMK/Rollo Pyro and Pyrocat
negatives is really significant because it shows that with graded
papers, which are very sensitive to blue light, the actual range in
effective printing densities between silver and UV printing is even
greater than would be suggested by the visual reading itself.
Sandy
>Sandy,
>
>I am interested in Pyrocat-HD for Arista400 (aka HP5), 8*10, in a
>JOBO, as a substitute for PMK I now use . I seem to recall that it
>will give a (much?) lower B+F ithan in PMK (which is substantial ).
>Is that true in your experience?
>
>Thanks,
>
>Cor
>
>-----Original Message-----
>From: Sandy King [mailto:sanking@clemson.edu]
>Sent: Wednesday, February 26, 2003 5:35 AM
>To: alt-photo-process-l@sask.usask.ca
>Subject: Pyrocat-HD
>
>Perhaps some of you have wanted to try Pyrocat-HD but were turned
>off by the prospect of having to mix from scratch. If so please note
>that you can now buy Pyrocat-HD in a pre-mixed kit from
>Photographers Formulary.
>
>If interested you can find the results of some testing at
>http://unblinkingeye.com/Articles/PC-HD/pc-hd.html
>
>Some of the testing there was provided by our list member Clay
>Harmon, who has used Pyrocat_HD enough to form some concrete ideas
>about its qualities.
>
>The Pyrocat_HD formula was first presented on one of the rec.photo
>newsgroups some years ago, with another name. In its present name,
>with some subsequent modifications, it was introduced by Judy Seigel
>in Post-Factory, as part of an article I did for PF on staining
>developers. The latest formula, which you can find at
>http://unblinkingeye.com/ , incorporates some minor modifications of
>the formula first published by Judy in PF.
>
>Pyrocat-HD offers some very real advantages for alternative printers
>over PMK and Rollo Pyro, especially with rotary processing, and I
>encourage you to give it a try.
>
>Sandy King
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