Zone System Testing When Using Pyro

When you're using PMK pyro and doing zone system tests, it's my understanding that the densitometer readings are taken with the blue filter in place (i.e. you need a color densitometer). Fortunately, I have a color densitometer. However, I'm not clear on exactly what the blue filter accomplishes. Is it supposed to "read through" the pyro stain, so that in theory at least the numbers you get with pyro would approximate the numbers you would get with a normal developer? I ask the question in part because as I've started doing the tests, I've gotten very high base plus fog numbers with devleopment times of 8 minutes or more, much higher than the numbers I got with times of 4 minutes and 5 1/2 minutes (I use Phil Davis' testing system, not "traditional" zone system methods). This despite taking the readings with the blue filter in place on my Macbeth color densitometer. I realize that base plus fog increases to some extent as development times increase but the difference here is much greater than anything I've seen using developers other than pyro. Since there is no exposure given to the base plus fog area of the film, I can only assume that the increase is caused by the increased staining as the development times increase but I thought the blue filter was supposed to more or less allow the staining to be ignored. If it does, then why is the base plus fog increasing so much?

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As an aside, the color wheel on my densitometer has two sides with identical colors on each side. The only difference is that on one side the letter "A" is next to the three colors. The instructions don't say anything about what the letter "A" stands for or what the difference is between the two sides of the color wheel. Does anyone happen to know?

Brian

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I know nothing about PYRO development. wish I did. But i do know

about densitometers. Most color densitiometers have two status

channels. Status channel M is for color negatives, and status

channel A is for transparencies.

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Kevin

Brian,

The reason you use blue with pyro readings is because the stain will

block the blue light. Since the stain makes up part of the image,

using the blue filter will allow you to read both the stain and silver

combo on the neg.

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Although I've never had that much base fog. Is your developer

fresh? I've always gotten a clear base on all negs, even on N+

situation (FP4, TMAX, HP5). One thing that you will notice is the

reduced speed that you;ll get from PMK.

Maybe your increased fog density is caused by aerial oxidation of the

pyro due to the longer development time. You could try a test

changing to fresh developer at 1/2 the time and seeing if the fog is

reduced.

The blue filter does measure the stain as well as silver density.

You then ideally correct the reading you get using a table, such as

that provided in Dick Arentz's Platinum Book, and I think in various

articles that have come out on the subject.

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The amt of base plus fog you get with Pyro is very dependent on the

film. It does increase with longer dev times, and is particularly

notorious for doing so with HP5+. This can become a prob with

processes/light sources which are blocked by the pyro stain, such as

UV/Platinum. The main issue I think is that you just get very long

printing times, which is one reason why a lot of people using pyro

for Pt/Pd go with Tri-X or FP4+ over HP5+. Are you using HP5+ by any

chance?

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Hope this helps.

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Nathan

Thanks to all who responded. I should have mentioned that the film is

indeed HP5+.