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  1. #11
    clay's Avatar
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    Quote Originally Posted by DrPhil
    Gee whiz,

    All I wanted to know was if a guy with a non-UV capable densitometer wanted to print on Pt/Pd could he use his blue wavelength measurements for determining proper development. This was all assuming the use of a non staining developer of course.

    Clay seems to have answered this question for me.

    The idea of using pyrocat HD to create dual purpose negatives is appealing. However, I also want to be able to measure what I am working with.
    What i did before I got the UV densitometer was just print the stained film test wedge on my palladium paper, and plotted the Visual density range against the resulting reflection density of the print. The steps won't necessarily be in the nice even 0.15 units, but the visual density range I would calculate worked just fine as a target DR for the process. I generally found that at pyrocat neg target VISUAL DR of 1.2 or so would give me a nice print that would be equivalent to a non-stained DR of 1.8. This is good enough for government work.

  2. #12

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    Quote Originally Posted by Kirk Keyes
    Sandy wrote, "The brown stain of Pyrocat-HD is a more effective filter for UV light than the yellow/green stain of the pyrogallol based PMK and Rollo Pyro."

    I suspect you will think I'm nit-picking, and I understand English is often not a very precise language, but I would like to point out that the "brown" color of a PyroCat HD neg and the "yelow-green" color of a PMK or Rollo neg do not predict negative absorbances in the UV. There's nothing intrinsically special about one stain appearing brown or yellow-green when considering UV.


    Kirk
    Actually I was being very precise. What I said about brown and yellow/green stain was made in the context of their UV trannsmission with specific developers, which I have tested. Note that I did not say that "brown stain" is a more effective filter for UV light than "yellow/green stain", but that "the brown stain of Pyrocat-HD" is a more effective filter for UV light than "the yellow/green stain of the pyrogallol based PMK and Rollo Pyro." The use of the definite article "the" in this sentences limits the scope of the comparision to the specific items identified.


    Sandy

  3. #13

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    DrPhil,

    Sorry about the brief diversion - I was short on time and I forgot to actually get to my point where I actually addressed your question.

    Yes - Clay did a good job with his answer - and notice that he said in part #2 - "D-76 negs respond to UV and Blue equally, unlike stained pyro negs."

    That was where my point was going - it appears to really depend on you choice of developer. As I said earlier, whatever Stouffer is using for the step wedge discussed below, there is a difference in the UV to blue/vis absorbance. Clay found that D-76 on his film makes no difference.

    So I'm just trying to point out 2 things - 1) you can't tell by visual tests/color what will happen with UV absorbance, 2) so you just have to measure it.

    Kirk

  4. #14

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    Donald wrote, "But Christ do you iron your shorts too?"

    Do you mean underpants/underwear shorts or knee-length or less than knee-length trousers?

  5. #15

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    Sandy wrote, "Actually I was being very precise. [...] The use of the definite article "the" in this sentences limits the scope of the comparision to the specific items identified."

    Sandy, sorry about that - you're right. I did much better on the math portion of the SAT than I did on the verbal portion.

    But I do want people to consider that we can't make assumptions about wavelengths which we can't see based on colors we can see. Tools for measurement are going to be needed to be certain. That may mean using a densitometer or using printing paper to determine density.

  6. #16

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    Quote Originally Posted by Kirk Keyes
    Donald wrote, "But Christ do you iron your shorts too?"

    Do you mean underpants/underwear shorts or knee-length or less than knee-length trousers?
    Kirk,

    Being the common uneducated type that I am that would translate to boxers or briefs depending upon your particular orientation. Hell I didn't even know that they made the other types. Thanks for broadening my knowledge base.

  7. #17
    Joe Lipka's Avatar
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    Favorite Developer questions usually elicit 2N responses where N is the number of photographers responding to your post. I will plug my favorite film developer D-23 (two bath variety) that can be used for silver as well as alternate processes. Used it for about twelve years and can make prints in silver and platinum/palladium from the same negative.
    Two New Projects! Light on China - 07/13/2014

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  8. #18

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    Quote Originally Posted by Joe Lipka
    Favorite Developer questions usually elicit 2N responses where N is the number of photographers responding to your post. I will plug my favorite film developer D-23 (two bath variety) that can be used for silver as well as alternate processes. Used it for about twelve years and can make prints in silver and platinum/palladium from the same negative.
    I don't question the fact that it is possible to make prints in silver and in pt./pd. from the same D23 negative, or from negatives processed in D76 or HC110 for that matter. But regardless of whether you use D23 one bath or two bath the end result is a negative that has the same effective printing density range for both silver and pt./pd. so if you optimize development for one process it will be necessary to resort to some type of contrast control for the other. The point of dual purpose negatives is that you can print in both processes without having to use any contrast controls. Granted that the use of VC papers in silver and Na2 in pt./pd. makes contrast control a fairly routine operation but my theory is that it is best to always start with the most optimum negative for the process(s).

    BTW, if you look in Edward Weston's daybooks you will find that the knowledge that pyro negatives could be used for printing with both silver and pt./pd. has been around for a long time because at one point he comments specifically on this subject.


    Sandy
    Last edited by sanking; 08-31-2004 at 11:27 AM. Click to view previous post history.

  9. #19
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    I want to say something intelligent on this point, but I'm not sure I know how. Anyway, sometimes the most intelligent thing to say is rather on the stupid side, in that it might stir up more intelligent answers.

    I don't know, for example, what the visible channel or the UV channel are measuring. I ass-u-me that the RGB channels are measuring something related to color separation positives for dye separation or similar processes. Do the specs for a commercially available densitometer provide spectral distribution plots of what these channels measure? If so, what does the visible channel have to do with photosensitive materials, when panchromatic films are more sensitive to red and blue than the eye? How much of the UV that is measured will get through the glass of a printing frame?
    Gadget Gainer

  10. #20

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    Quote Originally Posted by gainer
    I don't know, for example, what the visible channel or the UV channel are measuring. I ass-u-me that the RGB channels are measuring something related to color separation positives for dye separation or similar processes. Do the specs for a commercially available densitometer provide spectral distribution plots of what these channels measure? If so, what does the visible channel have to do with photosensitive materials, when panchromatic films are more sensitive to red and blue than the eye? How much of the UV that is measured will get through the glass of a printing frame?
    I have no specifications at all for what the RGB channels of my X-Rite 810 measure. For the Gretag D-200 there are no spectral distribution plots but I do have information as to the peak wavelength and bandwidth for Visible, Blue, Ortho, Green, Red, UV and Infrared. As I mentioned in another message the peak of the UV reading is 373 nm, and the bandwidth is about 45 nm, which means that nothing will be measured lower than about 350 nm or higher than about 395 nm. Ordinary float glass will pass over 95% of the light in this range and up to 90% at 300 nm. Float glass absorbs virtually all radiation below about 300 nm.

    Many alternative processes, including the colloids and metal salts, are highly sensitive to radiation in the 200-300 nm range, but for all practical purposes this light is of absolutely no use unless we devise ways of exposing without using glass between the light and sensitized material. And even if we devised such a means of exposure it would be impractical to use because of the extreme danger posed by UV radiation of this wavelength.

    Spectral Power Distribution charts are available for many of the UV light sources used in alternative printing. I have such charts for many of these lights, including BLB tubes and the USHIO metal halide bulb I use in a NuArc 26-Ik plate maker. Most of the radiation in the BLB tubes is between 350 -420 nm. The USHIO metal halide bulb also radiates a lot of energy in this range, but also puts out quite a bit of light above 420 in several spikes even up into the 500 nm range.

    So in practice the radiation useful to UV sensitive processes is in the 300 - 420 nm range, with a very rapid drop-off for both colloid and metal salt processes with longer wavelengths.

    Sandy

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