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Thread: Pyro Staining Index

  1. #1

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    Pyro Staining Index

    Hi, has anyone here played around with trying to figure out a system to calculate a "Pyro Staining Index"?

    My idea is to somehow compare the Contrast Index measured by measuring the blue channel densities and then comparing to say the green channel densities when developed to a particular CI. This could be as simple as dividing the results for the blue CI by the result for the green CI. So for a given hypothetical developer/film combo, one film would have an index of 1.2 vs. another that would be 1.35. This would show that the second film here has greater staining than the first one. This could be developed into a system to better quantify different developers or comparing films in any particular developer.

    Any one thought about this before?

    Kirk

  2. #2

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    Pyro Staining Index

    Kirk,

    I have never thought of calculating CI in this way. It might be feasible for some purposes but not for BTZS type testing because the index is constantly changing due to the proportional nature of the stain. This would make entry of step tablet values something of a nighmare because you would in essence have to apply a changing index to the values.

    In my opinion it would be more practical to find a filter that matches the effective printing density of the stain. The 47 filter, as noted in a different thread, passses some green light and provides fairly close results for VC papers but I suspect that you could find a broader band filter that passes more green light that would work even better.

    The subject is interesting but since I am primarily interested in AZO and alternative printing it is not one that I am likely to pursue further. I hope you do because there is a definite need for pyro users to uderstand better how the stain works with VC papers (and graded papers too for that matter). There is really a lot of misinformation being passed off as fact by people who should really know better.
    http://www.sandykingphotography.com/
    For discussion and information about carbon transfer please visit the carbon group at groups.io
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  3. #3

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    Pyro Staining Index

    Hi Sandy,

    I'm certainly interested in pursuing it further - thanks for your feedback!

    "It might be feasible for some purposes but not for BTZS type testing because the index is constantly changing due to the proportional nature of the stain."

    Do you mean the stain is constantly changing because of how the stain density changes when a film is developed to a different CI - N-plus or minus development? If so, I suggest the comparison be made at some standardized CI - take your pick of CI for the value.

    If you mean the stain is constantly changing because of variability in the development/staining process, then perhaps more work needs to be put into creating a repeatable development process - which after all is what the Zone System is all about.

    As an example, let's look at the charts you have on Unblinking Eye in your "An Introduction to Pyro Staining Developers" article. You compare FP-4 and several staining developers, all developed to about the same CI - 0.48 or so. There are distinct differences in the blue channel vs. the visible channel (as well as the UV). I believe the visible channel used here is close enough to using the green channel alone if desired for the sake of example.

    If I'm reading the numbers correctly, here's what I come up with by using simple division of CIs as I mentioned above. (Please excuse me trying to make a table in ASCII)

    Developer Blue Stain Index UV Stain Index PyroCat 2:2:100 1.13 1.26 PMK 1:2:100 1.31 1.29 WD2D+ 20:20:400 1.21 1.19 Rollo 2:4:100 1.19 1.23 PyroCat 1:1:100 1.16 1.36

    Comparing just the Blue Stain Index, we can see that PMK gave us the strongest index. And as the UV stain index, both PyroCat dilutions and PMK gave the strongest indexes. PyroCat with it's shorter development time than PMK is probably why you like using it for your alternative processes.

    You are right that base staining should probably be taken into account as it may severely affect printing times - any ideas on a system for that?

    But anyway, just looking at these simple Stain Index calculations, it looks like some useful info can be gleaned from them, and with out having to give a lot of other numbers that need to be reduced for easy interpretation.

    Kirk

  4. #4

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    Pyro Staining Index

    I'll try the table again (in ASCII of course!)

    Developer----------- Blue Stain Index------- UV Stain Index

    PyroCat 2:2:100--------- 1.13-----------------------1.26

    PMK 1:2:100-------------1.31-----------------------1.29

    WD2D+ 20:20:400------1.21------------------------1.19

    Rollo 2:4:100------------ 1.19----------------------- 1.23

    PyroCat 1:1:100--------- 1.16------------------------1.36

    Kirk

  5. #5

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    Pyro Staining Index

    " Do you mean the stain is constantly changing because of how the stain density changes when a film is developed to a different CI - N-plus or minus development? If so, I suggest the comparison be made at some standardized CI - take your pick of CI for the value."

    Yes, that is what I mean. The percentage of stain density compared to silver density at at given point on the step tablet changes according to time of development.

    Thanks for the further explanation about the contrast index. I now understand how you would apply it and I did not from your previous message. But bear in mind that neither the Blue channel or Visual channel is correct for printing with VC silver papers so it would still be highly desirable to make densitometer readings for these papers thorugh a filter that would more closely approximate effective printing contrast at a given contrast, say #2 1/2.

    "Comparing just the Blue Stain Index, we can see that PMK gave us the strongest index. And as the UV stain index, both PyroCat dilutions and PMK gave the strongest indexes. PyroCat with it's shorter development time than PMK is probably why you like using it for your alternative processes."

    Shorter development is just one of the reasons I use Pyrocat-HD instead of PMK for alternative processes. The long development times required with PMK for the CI necessary for alternative work is not only an inconvenience but also causes more oxidation and B+f stain, very undesirable in alternative work. You can also understand from looking at the indexes you extracted from the article that there is a much greater difference between the Visual/Blue index and the UV index with Pyrocat-HD, which makes ite better than any of the other developers for the so-called dual purpose negative, one that can be used for both silver and Pt/Pd.
    http://www.sandykingphotography.com/
    For discussion and information about carbon transfer please visit the carbon group at groups.io
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