New/different method for reversal processing of b/w films?

Discussion in 'Darkroom Developing and Printing' started by sreenath, Jun 28, 2007.

  1. sreenath

    sreenath Guest

    I am seeking comments from the newsgroup about a "new/different" idea
    that I have for reversal processing of b/w film.

    I thought of this method since I am hesitant to use potassium
    dichromate (I have a KG of this stuff unused
    for past 7 years), or potassium permanganate(sp?) and acids.

    Here are the steps:

    1. Expose and develop film
    2. Wash the film while it is still in the tank. DO NOT FIX.

    3. Use sulfide or thiourea to convert the remaining halide (this
    would be the positive image)
    Now the entire silver halide has been converted to either silver
    metal(because of development) and
    some sulfide. There is no more halide left in the film.

    4. Use rehaloginating bleach (ferricyanide+ bromide) This will convert
    the metallic silver(-ve image) to halide.

    5. Fix the film. Negative image is removed by the fixer, and the
    positive image, in form of silver sulfide
    remains. Sepia toning is already done!

    My question is, would this work?
    The major question is about step 4. I am assuming that the
    rehaloginating would convert just the silver, but not the
    silver sulfide.

    Is this assumption valid?
    I know this is a round-about way of reversal processing, if at all
    this works, but I am still curious.

    thanks for your comments,
    Sreenath
     
    sreenath, Jun 28, 2007
    #1
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  2.  
    Richard Knoppow, Jun 28, 2007
    #2
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  3. Your reasoning is correct. I don't know why this has not
    been done in the past. It was common to use a solution of
    sulfide to redevelop in reversal processing. I think this
    would work here also although its possible that the
    ferricyanide bleach would not convert all of the silver. I
    think it deserves to be tested. There are a number of old
    formulas for toning motion picture and slide films with
    stronger bleaches than are used for sepia toning prints, one
    of them might work. AFAIK, silver sulfide is not affected by
    ferricyanide bleach.
     
    Richard Knoppow, Jun 28, 2007
    #3
  4. sreenath

    sreenath Guest

    Thanks for your views.
    I will test this one of these days and post the results.

    -Sreenath
     
    sreenath, Jun 29, 2007
    #4
  5. If you look at how color reversal is done your idea is
    rather similar. In color processing its not necessary to
    remove the silver from the negative image until the very
    last step. What makes this possible is that the first
    developer does not react with the color couplers to produce
    dye but the reversal developer does. So, the film is
    developed first to get a negative silver image wit no dye
    then developed again in the chromogenic developer. Since the
    only halide left for the second developer to work on is what
    is left over from the first developer the result is a
    positive silver image along with the dye image. The silver
    is removed by a bleach leaving the dye behind. Your idea
    also proposes two different developers, the first the normal
    negative developer producing a negative silver image, the
    second a developer, namely the sulfide, which converts the
    remaining halide to silver sulfide but does not affect the
    first, silver, image. Then, if the metallic silver image is
    removed using a bleach which does not affect the sulfide
    image the resulit should be a sepia colored positive image.
    This really should work.
     
    Richard Knoppow, Jul 1, 2007
    #5
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