UV vs visible in non-pyro negatives

Discussion in 'B&W: Film, Paper, Chemistry' started by DrPhil, Aug 29, 2004.

  1. DrPhil

    DrPhil Member

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    Over the past month I have developed over 150 negatives in pyrocat. One thing that I have noticed from reading about pyro is that many use it for alt processes. As I understand it, the stain responds differently to UV wavelengths over the visible (mostly blue) wavelengths used in enlarging. Apparently many people use pyrocat negs for dual purpose silver and platinum/palladium. My question is how do non-pyro negatives work with alt processes? For example, will a D76 1:1 negative respond to UV and Blue wavelengths equally?
     
  2. clay

    clay Subscriber

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    D-76 1:1 negs will work fine if processed to the appropriate density range. I have many nice palladium prints from D-76 developed negatives. Because they have a density range of 1.8-1.9, they would be impossible to print in silver. My UV densitometer gives the same visual wavelength density range as the UV wavelength density range for D-76 negs. Stained negatives, on the other hand, read VERY differently on the visual channel than the UV channel. My nice stained negatives with a UV density range of 1.9 only have a visual wavelength density range of around 1.3, which is very printable on grade 2 or grade 1-1/2 paper.

    So the answer to question 1 is : They will work fine if processed appropriately and the answer to question 2 is: yes, D-76 negs respond to UV and Blue equally, unlike stained pyro negs.
     
  3. sanking

    sanking Member

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    Most alternative processes need a light source high in UV light, although many of them also have some sensitivity to light in the near UV, violet an blue. The stain of Pyro negatives functions as a very strong actinic filter to UV light and increase the effective printing contrast. Negatives developed in non-staining developers such as D76, HC110, etc. pass UV and Blue light about equally well.

    The dual-purpose is possible with stained negatives because the effective printing density is much greater for UV processes than for Blue sensitive processes. For example, a typical FP4+ negative developed in Pyrocat-HD for about seven minutes will have an effective printing density range of about 1.05 for Blue light but around 1.35 for UV light. You could print this negative on a grade #2 silver paper and also with a standard 25/75 mix of pt./pd. with just a small amount of contrast control.

    Sandy
     
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  4. gainer

    gainer Subscriber

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    First, pyro by itself usually refers to pyrogallol. Pyrocat HD uses pyrocatechin, AKA catechol or pyrocatechol. The stains are of different color. Both stain images are more dense to UV light than to visible. One of the advantages quoted for pyrogallol, specifically PMK, is that it can be used equally well on VC and alternative process. The alternative processes generally require a higher contrast negative because they are printing-out contact processes that are self masking. The yellow stain image adds much more to the contrast under blue or UV light than it does to visible or blue-green light. The differential may be in the other direction when comparing pyro prints on graded paper with alternative processes.

    Pyrocat may not be as much different. You will have to ask Sandy King.
     
  5. gainer

    gainer Subscriber

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    I see that while I was mulling over what to say, Sandy said most of it and some I didn't say.
     
  6. sanking

    sanking Member

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    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. There is consequently a larger difference between Blue printing density and UV printing density with Pyrocat-HD than with these developers, and when the goal is a dual purpose negative the larger the difference the better.


    Sandy
     
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  7. Kirk Keyes

    Kirk Keyes Member

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    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.

    One cannot make assumptions on the absorbance of a material in UV simple by looking at the color of that material in any visible wavelength. I think we all saw that demstonstrated with Sandy's comparison of UV measurements of his Kodak and Stouffer step wedges. Sandy said all of his tablets looked pretty neutral in visible light, but his Stouffer tablets transmitted more in UV than the Kodak one. Who would have guessed this by looking at them?

    So what I'm trying to point out here is that your sentence would be more accurate by saying, "The stain of Pyrocat-HD is a more effective filter for UV light than the stain of the pyrogallol based PMK and Rollo Pyro." Or pehaps, "The stain of Pyrocat-HD, which happens to appear brown, is a more effective filter for UV light than the stain of the pyrogallol based PMK and Rollo Pyro, which happens to appear yellow-green."

    Nit-picky, perhaps, but it is an important principle to remember none-the-less.

    Kirk
     
  8. Jorge

    Jorge Inactive

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    I disagree with you on this one Kirk. From color theory one would expect a "green" or yellow/green filter to transmit more blue light spectra than a yellow or brown filter as such it is not far fetched that it would block more UV as well. Visual observation should give us a strong indication of the "probable" behavior of the stain. Of course this would then have to be verified with the appropriate measurements.

    As to the behavior of non staining developers, Clay had it right, pyrocat, pyro etc have the "ability" to be used for both silver and alt processes. OTOH my recent test of TMX400 with HC110 show similar results to Clay's. UV absorbtion is proportional to the amount of density or perhaps I should say silver halide content.
     
  9. Donald Miller

    Donald Miller Member

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    Picky, Picky, Picky!!!!

    I understand the point that you are making in regard to the proper expression of what Sandy was saying. But Christ do you iron your shorts too?
     
  10. DrPhil

    DrPhil Member

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    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.
     
  11. clay

    clay Subscriber

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    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.
     
  12. sanking

    sanking Member

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    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
     
  13. Kirk Keyes

    Kirk Keyes Member

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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
     
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  15. Kirk Keyes

    Kirk Keyes Member

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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?
     
  16. Kirk Keyes

    Kirk Keyes Member

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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.
     
  17. Donald Miller

    Donald Miller Member

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    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.
     
  18. Joe Lipka

    Joe Lipka Member

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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.
     
  19. sanking

    sanking Member

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    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
     
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  20. gainer

    gainer Subscriber

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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?
     
  21. sanking

    sanking Member

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    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
     
  22. Kirk Keyes

    Kirk Keyes Member

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    That's why we need to check with the manufacturer and see if they list the specifications for our particular instruments. As Sandy shows with his Gretag D-200 II, they are very specific in this information. Xrite says that his model 810 densitometer uses Status A color filters for reflection and Status M color filters for transmission. I have a MacBeth TD-903 Transmission densitometer that has both Status A and M color filters for transmission. My Noritsu DM-201 uses Status M for transmission. As you can see, each manufacturer may take a different apporach.

    So what are Status Filters? The following is taken from a Tobias densitometry technical bullitin:

    Spectral Response
    The reflection densitometer uses similar color filters to those that produce the separations. So you might think that different densitometers would read the same. However, there are some differences in the filters of various types of densitometers causing discrepancies in readings between units. To overcome this, ANSI specifications have defined several system responses for densitometers. Units conforming to these specifications should have a reasonable agreement. Among these spectral responses are Status A and M which are used in photographic applications and Status T, which is generally accepted as the Wide Band Graphic Arts response in North America. European responses are different giving a higher reading on yellow ink; this response is called Status E. Other responses exist such a Status I which is a narrow band response. Because these varying system responses exist, it is important that the Status response of the densitometer that you are using be included in any communication between customer and vendor. (End of Tobias Quote)

    Note that last sentence - that was something I mentioned in the other, long thread while I we were discussing the calibration of densitometers.

    According to the Kodak Filters for Scientific and Technical Uses book I have from 1980, Status A and M filters "are carefully selected and calibrated to conform to close spectral tolerances. Their use allows more direct comparison of measured densities with other similarly equipped electronic densitometers." It also says they must be used with the #301A IR cut-off filter.

    Kodak does not sell Status filters despite making them - they must be purchased from densitometer manufacturers (at least in 1980...).

    From the Wratten book, it looks like the Status filters are based on the Wratten #92 for Red, #93 of Green, #94 for Blue. The book does say the 92/93/94 combo is used for densitometric measurements of color films and papers. However, it points out that like all Wratten filters, the precision of these filters is +/- 5%. Perhaps it is these #92/93/94 filters that are being "selected" for use in the Status filters. The then goes on to say that it recommends using a #301A Infrared rejection filter in combination with these filters as they all pass IR.

    For less precise work, one could use the narrow band color filters could also be used - the #25 for red, #61 for green, and the # 47B for blue. These filters are often used for making color separations with B&W film, but they will not match the characteristics of the Status filters

    See my last paragraph above. The Kodak book I mentioned above has graphs of the spectral response of all the filters it covers including the Wratten #92/93/94 densitometric color filters I discussed above, but unfortunately not the Status color filters . Gretag gives enough info about the filters in the D-200 II that we could graph the spectral response.

    Excellent question! I'm not really sure if a filter is used with all densitometers when they say "Visual" but I suspect there is. The Gretag D-200 II does use one for visible readings - the manual says it has a filter that is centered at 555 nm, has a bandwith of Tmax/2 of 100 nm and Tmax/10 of 180 nm. So most of the light it is seeing is from around 505 to 605 nm, and it will not see anything below 465 nm or above 645. So it is missing all of what would be considered the Violet, Indigo, and Red portion of our visual response (depending on who's wavelength ranges you choose for each color).

    Now there may not be anything really wrong with that, especially since Gretag has told us that this is the property of the filter they chose to use. But is may be a concern as you say if your film is more sensitive to red than blue and your densitometer is not measuring any red but is measuring some (albeit only a little) of the blue...

    But we also need to keep in mind, that we need to pick the filter we are using to try and best match the conditions we are making these measurements for. If you have a relatively neutral material for the range we are making an exposure, say a step wedge, then it will not really matter much if our Visual filter does not cover the entire range. You would get comparible results if the material is fairly neutral. It is when we start measuring things that have significant colors in them that this will come into play and then be a big issue.

    If anyone has access to the old ANSI specs for these things, I would love to see them. Or the current specs either...

    The float glass I've measured starts to drop significantly around 360 nm and is pretty much opaque by the time you hit 300 nm. These wavelengths are lower than I gave in the other thread. I'm in better agreement with Sandy on this issue now than I was in the other thread...
     
  23. sanking

    sanking Member

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    Kirk,

    Do you know how Tmax/2 and Tmax/10 are derived? I assumed that the equation was maximum transmission divided by 2 or 10. But if this is so, how does one determine the figure for maximum transmission? Would this by default be 100%?

    Sandy
     
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  24. Kirk Keyes

    Kirk Keyes Member

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    Sandy, yes, you are right in those assumptions. A spectral transmission chart is made for the filter comparing wavelength vs. absorbance (or transmission - it doesn't make much difference since transmittance and absorbance are directly related to each other).

    The wavelength at which the maximum tranmittance occurs is noted. This will probably be close to the "dominant wavelength" of the filter, or its "hue" as seen with our eyes. (Note, the dominant wavelength will shift a few nanometers depending on the color temperature of the light source, the maximum transmittance will not change with color temp. The dominant wavelength also relates more to how the eye sees colors on the color wheel than what its maximum transmittance is.)

    The chart can then be "normalized" by setting the tranmittance at that wavelength to be 100%. All the other transmittance values for each wavelength will then be adjusted by the same ratio as was used to set the 100% point and we can make a new chart.

    So now you have a chart that has been "normalized", with the wavelength of maximum tranmittance at 100%. To find the Tmax/2 point, look for where the plot of the filter crosses the 50% tranmittance mark. For a band-pass filter like we are describing here, we hopefully have a filter that "cuts-off" sharply and is fairly symmetrical. Think of a steep, sharply sided Bell-curve used for grading papers or in statistics, the shape should be similar.

    The #93 and #94 Blue Wrattens both do this, but the #92 Red only cuts-off on one side! It has a transmittance of only 0.40% at 620 nm, a dominant wavelength of about 645 nm where it transmits about 60% but it has a peak transmittance of 88% at 700nm. But it does not drop off on the Infrared side. They must be assuming that since all of the filter in this series must be used with a #310A IR cut-off filter, the IR-blocking filter will take care of that side (it starts to filter out at around 680nm.)
     
  25. Kirk Keyes

    Kirk Keyes Member

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    "How is the film's spectral sensitivuty linked to the densitometer's?"

    It's not. I don;t have time for a longer answer now....

    Kirk
     
  26. gainer

    gainer Subscriber

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    TMX and some other panchromatic films are used to make color separation intermediates. I would expect that the individual RGB channels would be of use in their production. I cannot see a use for a visual channel off hand. What I find mising in this thread is what is necessary to make the transmission characteristics of the various filters come true. When a certain fiter of known transmission spectrum is used it is either known or assumed that the spectral response of the photocell is uniform across the photographic spectrum. IOW, the transmission spectrum of the filter is not the whole story.

    I know of no photosensitive materials that are uniformly sensitive across the complete range of the films and papers we use. Unless I know that the native response of my densitometer is the same as yours, I cannot guarantee that the result I might get by measuring through a given filter will be the same you would get from your measurement of the same densities.