How does anti fog work?

Discussion in 'Color: Film, Paper, and Chemistry' started by cinejerk, Mar 22, 2012.

  1. cinejerk

    cinejerk Member

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    Just wondering how anti for agents work. In particular benzotriazole.
    Can this chemical be incorporated into any developer? Color as well as b&w?
     
  2. DREW WILEY

    DREW WILEY Member

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    Someone else can explain the chemisty, but from a functional standpoint benzotriazole is a restrainer
    which can be used with either film or paper. It is also used as a substitute for potassium bromide when a cooler image tone is desired, but always use less - maybe a fourth as much in grams.
    And it takes very little to clear fog in film (too much and you'll cut the thin areas of the neg too).
     
  3. DREW WILEY

    DREW WILEY Member

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    Sorry, but I missed the main question. Sounds like voodoo for color work ... never heard of that!
     
  4. cinejerk

    cinejerk Member

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    I have seen benzotriazole used in E6 first developer. Maybe it wasn't used as an anti-fog for that purpose?
     
  5. Mike Wilde

    Mike Wilde Member

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    In colour I am pretty sure that there are other agents other than BZT, as I term it, and KBr.

    There is a chemical I abbreviate HAS (mid age brain fart- full name won't come to me right now - maybe hydro azole sulfate; there is also a hydrocloride salt version ) that scavenges colour couplers to keep 'too much' of a colour forming once some colour couplers and dye formers start acting.

    Dyes form as a result of respective latent electron energy stored in the silver halide in the particualr layer of the colour film being reduced to elemental silver, which along the way oxidizes the developer.
    The oxidized developer components link with the dye formers that are also in the similar layers as the silver layer we are talking about here to form their particualr hue.

    The amount of colour ( ie a type of contrast in colour photography) a given type of colour paper produces can be modified by fiddling with the chemistry of the developer and that is kind of akin to a restriner's action in other ways in b&w.

    Citrazinic acid lowers contrast (this I have experimented with) and 'H' acid, as PE calls it, raises contrast. I have yet ot figure out what is in H acid though.

    I hope this helps.
     
  6. cinejerk

    cinejerk Member

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    Ok thanks Mike.
    Yep, a lot of chemistry going on here.
    I know I saw it in a color developer recipe somewhere.
    If I find it I'll post it.

    Here is one.

    E-6 first developer
    cf. Wiellette, Zone V, Inc. This developer was supplied in Zone V kits for several years. This formula has worked consistently well for general use photography. Follow the suggested variations to achieve different results.

    Note also that the latent image properties for reversal films are not long lived. While black & white and some C-41 films may hold their latent images for a long time (years), reversal films are unlikely to retain their latent-image color balance over long periods.

    Water 110F 900 ml
    Sod. Sulfite anhyd. 23 g
    Hydroquinone 6 g
    Metol 2.5 g
    Phenidone 1% solution 50 ml (65 ml 1% Dimezone-S)
    Sod. Carbonate anhyd. 18 g
    Pot. Bromide 1.8g
    Sod. thiocyanate 5% solution 20 ml (2.5ml 40% soln.)
    Benzotriazole 0.2% solution 50 ml
    Pot. Iodide 0.2% solution 5 ml
    Water to make 1 liter

    Set pH = 10.0
    Notes:
    To decrease yellow: increasing thiocyanate 0.1 g produces a very noticeable change. To increase yellow: decrease thiocyanate 0.1 g.
     
  7. newcan1

    newcan1 Subscriber

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    Kodak ECN-2 developer contains an anti-foggant, Kodak Antifoggant AF-2000. I have another thread going here where Photo Engineer has commented on my desire to experiment with more readily available chemicals, and he suggested I try a little benzotriazole instead of AF-2000. I should know soon how that works out - I mixed a batch and just need to shoot a test roll or two.
     
  8. nworth

    nworth Subscriber

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    HAS is hydroxylamine sulfate. In black and white, it is a poor but harsh developer that usually creates a lot of fog. In color, it seems to act differently, restraining fog and clarifying colors. I don't really know the mechanism, the dynamics, or the details of its action. Citrazinic acid is often referred to as a neutral coupler. It competes with the regular couplers but produces colorless products. It helps regulate the color and helps control the action of the DIR couplers. I would think its concentration would be very critical and quite dependent on the type of film. Obviously E-6 films all have to be designed with this in mind to work universally with the E-6 process. HAS is not used in modern motion picture formulas, and may not be used in their still fill counterparts. However, ethylenediamine is found in them. I'm not sure exactly what it does. Color reversal first developers are very similar to black and white reversal first developers, but, of course, they are tuned to the color films and process.
     
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  9. Photo Engineer

    Photo Engineer Subscriber

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    Here are some facts;

    1. HAS is a developer preservative as well as a B&W developer. It is used mainly in color developers.

    2. The E6 first developer formula above is totally wrong in developing agents, pH and etc. I would not use it. If you are interested enough in altering it in the direction of "reality" look at the MSDS.

    3. Antifoggants are restrainers and can be used in color or B&W but in color they often cause color shifts unless other changes are made to compensate.

    Antifoggants include Benzotriazole (BTAZ), Phenyl Mercapto Tetrazole (PMT) and 5 Nitro Benzimidazole Nitrate to list the 3 most prominent. Each must be fine tuned for developer and for film.

    PE
     
  10. nworth

    nworth Subscriber

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    AF2000 is the only "strange" ingredient in the ECN-2 developer. Considering the number of people trying to use Vision-3 materials for still work, is there a substitute or an convenient source?
     
  11. Photo Engineer

    Photo Engineer Subscriber

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    There have been several names for AF 2000, including the possibility of typographical errors. This has been discussed extensively in other threads.

    IDK what the correct chemical is, but it appears to have some antifoggant or preservative properties.

    PE
     
  12. hrst

    hrst Member

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    Something called "AF9" was used before AF2000. It was solid, and IIRC, it was stated that AF2000 was introduced because of instability/risk of explosion of AF9. Maybe that would give some hint...

    Anyway, if you take a look at Kodak h2408 (for example, http://sysdoc.doors.ch/KODAK/h2408.pdf ), you will see that the effect of removing the antifoggant is quite minimal; +0.04 in blue low densities. So, it's mostly for "fine-tuning" towards the perfect result, and you probably won't see any difference unless you do a careful side-by-side test. To put this in perspective, the error caused by removing the antifoggant may be below the normal operational tolerances of a motion picture lab.