Changing color sensitivity of film.

Discussion in 'Silver Gelatin Based Emulsion Making & Coating' started by richard ide, Oct 29, 2006.

  1. richard ide

    richard ide Subscriber

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    One can hypersensitize film to increase effective film speed before or after exposure. My question is: Can the color sensitivity be changed in somewhat the same manner; or is that only possible when coating the film? I realize that it would have to be done with a dye rather than a vapor bath. My reason for asking is that ortho emulsions do not excel at cloud photography.

    Thanks

    Richard
     
  2. Photo Engineer

    Photo Engineer Subscriber

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    You can change the color sensitivity by the use of spectral sensitzing dyes. They are typically added just before coating the emulsion, but old workers used to bathe the film in the dye solution.

    You can dye in the blue, green, red, short IR and long IR regions of the spectrum. You should not try to dye a predyed film. So, if you have a pan film, you probably cannot undo the pan sensitivity and make it ortho, nor could you easily add an IR dye and make an IR film, although adding is possible under some circumstances.

    PE
     
  3. Gerald Koch

    Gerald Koch Member

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    The two reasons, that I can think of, that people use ortho films are that they like the films color response and/or they want to develop by inspection. If you add a red sensitizing dye to an ortho film you will lose both reasons to use an ortho film. If you have difficulty in rendering clouds with an ortho film why not just use an panchromatic one instead?
     
  4. Ryuji

    Ryuji Member

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    You can dye factory-manufactured film to modify spectral sensitivity. Some dyes require lower adsorption density to be effective than others, and these are the ones you want to use if you want to apply a dye on pre-manufactured materials. Many infrared dyes can be used in this fashion but there aren't many dyes for visible light that can be used effectively for this application. If what you want is panchromatic, it's easiest and probably cheapest to buy the finished film. Good cyanin dyes aren't cheap.

    But there are people who soak pan film in infrared dye bath to make infrared films. Big PITA but that is an option for nice fine grain IR film after discontinuation of Sakura (Konica) IR 750.
     
  5. wirehead

    wirehead Member

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    Can you post a link to more details on this?
     
  6. Photo Engineer

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    Doing this is not a *good* idea. You have to do it in such a way as you displace the dye already on the film, and sometimes it does not work or does not work the way that you want.

    Sometimes a "J" aggregate forms causing a shift to longer wavelengths and giving an unwanted spectral sensitization.

    Even worse, sometimes the dye sticks to the emulsion and leaves a severe stain in the negative.

    BTDT. Sorry.

    PE
     
  7. Ryuji

    Ryuji Member

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    I don't have a web page describing this technique, but it's a common trick among infrared community (as there are a couple of very good infrared dyes for this technique). A common method is to make 0.05% dye solution in 91% 2-propanol or methanol, immerse film for a predetermined period (say 2 min) and dry at once. This level of dye is sufficient for some of post-1930 infrared dyes but vastly inadequate for many dyes, so you have to select the dye very carefully. Again, I don't recommend doing it if what you want is panchromatic emulsion. Just buy it in that case.
     
  8. Photo Engineer

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    If you do what Ryuji suggests, work in total darkness for the entire operation of re-dying, drying, loading into the film holder (or whatever) and then the dark steps of processing. Be aware that you may encounter drying spots on the film and that the dying process may wash the acutance and AH dyes out of the coating depending on the type of dye already present and the type of solvent you use.

    Don't expect stellar results. It may not work.

    Being one of the few here that has done spectral sensitization routinely, I am familiar with the pitfalls of this. In fact, I doubt if anyone has done this with really good results.

    PE
     
  9. Helen B

    Helen B Member

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    This is well outside my knowledge and experience, so all I'm doing is passing on this link which has contributions from Ryuji as a starting point for a bit of web surfing for the sake of interest (I hope that Ryuji doesn't mind me linking to that thread).

    You could also google 'diethylthiatricarbocyanine sensitization', as I did to find the above, or 'diethylthiatricarbocyanine' or similar and follow links. Tadaaki Tani calls it ‘Dye 8’ in ‘Photographic Sensitivity’. It is dye 69 in Mees, who also gives examples of the spectral sensitivities of a chlorobromide emulsion sensitized with a number of infrared sensitizers.

    Best,
    Helen
     
    Last edited by a moderator: Oct 31, 2006
  10. Ryuji

    Ryuji Member

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    That's right, and good job on finding it! 3,3'-diethylthiatricarbocyanine iodide is a good dye, and if used on undyed emulsion, it can be used with dim green safelight because of deep spectral notch. (But if you begin with panchro emulsion, work in total darkness.)
     
  11. Photo Engineer

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    Just remember that some of these dyes are not easily gotten and if available will cost about $100 / gram. There are few commercial sites that offer such dyes. Kodak, Fuji, Ilford etc. will not sell them at all. At one time, Kodak listed about 15 of them in their catalog, but no longer.

    One gram will be nearly a good supply for 2 reasons. You use very little dye in one experiment and the dyes have poor shelf life even refrigerated or frozen. This is especially true of infra-red dyes.

    I'll leave it to Ryuji to tell you where to get them.

    PE
     
  12. htmlguru4242

    htmlguru4242 Member

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    Ryuji, that's interesting.

    Are there, a)., any sources of that dye, and, b)., and cheaper dyes that can be used?
     
  13. Ryuji

    Ryuji Member

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    (a) Again, this is not a typical hobbist project. This dye is relatively common because some laser researchers use it, but I don't know of a source that an average hobbist can deal with.

    (b) No, good dyes in small quantity cost upward of $50/g in most cases. Good sensitizing dyes aren't easy or cheap to synthesize, and considering the number of steps and work involved, I'd gladly pay the money, although it's not exactly cheap.
     
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  15. htmlguru4242

    htmlguru4242 Member

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    Well, considering that you're talking about solutions that are on the order of 0.05%, $100 / gram is actually not that bad.

    Assuming that one were to obtain the dyes, how difficult would the actual re-sensitization be?
     
  16. Ryuji

    Ryuji Member

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    If what you want is to get decent infrared effect by soaking Pan F Plus or Plus-X or whatever in to the solution, you can get it with a couple of trials, if you already mastered the usual technical matters of infrared photography. (If you are not there yet, get a few rolls of HIE first--It'll save you from disappointment and frustration in the beginning.)
     
  17. Helen B

    Helen B Member

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    As I suggested in my last post, it is worth doing a web search on diethylthiatricarbocyanine. You will find sources, and other information.

    Best,
    Helen
     
  18. htmlguru4242

    htmlguru4242 Member

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    I've definetely shot enough IR film to have a good handle on what to do, but now that HIE upwards of $10 / roll, this sounds like an interesting idea.

    They dye that was menioned in Helen's post is only $56 / gram at Sigma-Aldrich.
     
  19. Photo Engineer

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    Well, that sounds reasonable, but you will need to run several experiements to determine if it works, and you may need a spectrosensitometer to check out the real spectral sensitivity after you do the dying.

    Since we have no concrete source of dye, other than Sigma Aldrich, then that is the only common dye avaialble to us. Thanks Helen. I tried Kodak's current chemistry list and all of their sensitizing dyes formerly listed are no longer available.

    I currently have samples of about 10 dyes which are only for the visible portion of the spectrum and will not help with this problem.

    PE
     
  20. Helen B

    Helen B Member

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    From Mees, for interest:

    [​IMG]
     
  21. Photo Engineer

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    Helen;

    That is good for an approximation only. As it says, this is for a chlorobromide emulsion and all film emulsions that I know of are bromoiodide, therefore the spectrum and reactions will be different.

    These particular dyes may not even work on a bromoiodide or they may form "J" aggregates. We had tables of dyes with emulsions, pH, pAg and etc at EK that could be used to pick and choose.

    PE
     
  22. richard ide

    richard ide Subscriber

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    Wow, what interesting responses! Thank you all. My reason for originally asking, is that I have enough Kodak aerial dupe film (type 2430) to give me several thousand sheets; but it is blue sensitive. I want to do some experimenting with a very high resolution Wild lens I have and would prefer a panchromatic film but with the resolving power of type 2430.
    Which begs my asking another more convoluted question.
    Is the change in emulsion sensitivity on a molecular level or is it caused by the physical presence of the dye acting in somewhat the same way as a filter? And if so would the use of an optical filter in the image path perform a similar function?
     
  23. htmlguru4242

    htmlguru4242 Member

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    I think that the dye's function is to capture wavelengths of light to which the silver is not sensitive and donate electrons to the silver in the emulsion

    They definetely act on the molecular level.
     
  24. Photo Engineer

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    To be effective, a dye must initially have 2 properties. It must first be colored opposite to the wavelength you wish to sensitize the emulsion to, therefore a green sensitizer will be magenta in color and etc. Second, it must adsorb onto the surface of a silver halide grain. These are the two basic properties.

    The third property, acting after the first two, is the ability to pump the energy absorbed by the dye into the grain as if the photon were hitting the grain, so a blue or UV sensitive grain would become green sensitive by adding a magenta colored dye to the grain. The emulsion is still blue sensitive, so you end up with blue-green (ortho) sensitivity by adding a green sensitizing dye.

    The two simplest dyes are chlorophyll, a weak red sensitizer, and erythrosine a fair green sensitizer. Using erythrosine will give you an ortho emulsion from a blue sensitive emulsion if added properly. Erythrosine is the active ingredient in some food dyes and also in the old antiseptic Mercurochrome.

    PE
     
  25. Helen B

    Helen B Member

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    I only posted it 'for interest', not even 'for information' never mind 'for production' - but you are right to clarify the practical uselessness of it!

    If anyone would like copies of short extracts on the mechanism of spectral sensitization by dyes from Mees (readable) or Tani (a little less readable, more detailed, but still not exactly a DIY handbook) for their personal use - ie not for publication on the web - let me know.

    Best,
    Helen
     
  26. Photo Engineer

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    I have posted some of my wedge spectrograms and described my spectral sensitization experiments here on APUG somewhere. If anyone is interested in them, they may look them up.

    Spectral sensitization of a raw emulsion either before or after coating is one of the simplest of operations on an emulsion you can do, once you have a known good dye. Remember, that is a raw blue sensitive emulsion, not one already dyed. It also requires a good dye for the emulsion you are using.

    PE