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  1. #1

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    Potassium Dichromate bleach shelf life

    I use a modified version of the Kodak R-9 potassium dichromate bleach recipe for bleaching black and white _reversal_ Plus-X, Tri-X, and Fomapan R movie film.

    Can anyone tell me what is the shelf life of the mixed bleach? What about capacity for reversal purposes? It gets very cloudy with lots of sediment quickly when used for movie film reversal bleaching. I store the used R-9 in a separate container from the clean unused bleach, but I typically only use it for three or four 50 foot rolls of 8mm film before dumping it since I'm unsure of the capacity or the effect of the cloudy sediment.

    Here is the formula I use.

    Kodak Bleach R-9

    Water 1.0 L
    Potassium Dichromate (anhydrous) 9.5 g
    Sulfuric Acid (Concentrated)* 12.0 ml

    * CAUTION: Always add the sulfuric acid to the solution slowly, stirring
    constantly, and never add the solution to the acid; otherwise, the solution
    may boil and splatter the acid, causing serious burns.

    Note: I substitute 36 ml regular automotive battery acid for the 12.0 ml
    concentrated Sulfuric Acid since battery acid is about 1/3 the concentration of concentrated Sulfuric Acid. I've also read that you can substitute 66g Sodium Bisulfate for the Sulfuric Acid, but I haven't tried it.

  2. #2

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    It should last for at least a year in a well capped brown bottle. You have nothing to worry about. OTOH you do have to worry about exhausting the dichromate every time you bleach.

  3. #3

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    Thanks, Jorge. Is there a test for exhausted dichromate? How will I know when it is exhausted?

  4. #4

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    Quote Originally Posted by SkipA
    Thanks, Jorge. Is there a test for exhausted dichromate? How will I know when it is exhausted?
    It should turn green, meaning the Cr ox state is now III.
    Anyone correct me if I'm wrong, I'm still learning...

    SkipA, you have all my admiration for handling such a nasty chemical: you certainly know that all Cr(VI) compounds are carcinogenic at least.
    Can you share with me the process you're currently using for makeing b&w slides?

  5. #5

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    Hi Alessandro. Yes, I'm aware that potassium dichromate is carcinogenic. I wear a filter mask when mixing chemicals and use gloves when handling solutions.

    I'm not making b&w slides, though. I'm processing black and white reversal Super 8 movie film in 50 foot rolls using the Kodak procedures and formulas on their web site. Note that these particular emulsions are intended for reversal processing. It might work work with negative film, but I've never tried it.

    Here is the link to the Kodak H-24 Module 15 page for processing KODAK Black and White Motion Picture Films. This link is the one for the older D-94 / R-9 / D-95 process. You want to look at section three -- Reversal Films:

    Kodak Motion Picture Films Module 15 Processing Black-and-White Films

    Interestingly, the html version of the module gives the D-94 / R-9 / D-95 process, while the downloadable PDF file on that page gives the newer D-94A / R-10 / D-95 process. The R-10 bleach is a permanganate bleach, whereas the R-9 bleach is potassium dichromate.

    You'll find processing steps, times, formulas, and other information you need for reversal processing of Plus-X and Tri-X movie film. I've never tried it with Plus-X or Tri-X negative film. It should give you an idea where to start if you want to give it a try, though.

  6. #6

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    Most B&W films can be reversal processed. An important concern is using a film with a colorless or near colorless base. This limits the number of suitable films.

  7. #7

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    Hmmmm. So Tech Pan, for example. Maco Infrared film? Anyone tried reversing it?

  8. #8
    htmlguru4242's Avatar
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    I've had my bleach mixed up for a few months and its still going strong. I got it as a concentrate in clear bottles that are somewhat (maybe 5 - 8 years) old, and it was still good.

    Can you share with me the process you're currently using for makeing b&w slides?
    I do reversal processing of negative films, mostly with Tri-X.

    The process is actually pretty simple. I use D-76 as the developer, in a 1:1 dilution for the first developer and a standard dilution for the second developer. BASICALLY, the process is as follows: I expose a bit under the suggested ISO (I use 320, not 400) Also, I use a sodium dichromate bleach, but it is for all intents and purposes the same (in this case).

    1.) First developer - D-76 1:1 - 9:30 @ 68F
    2.) Stop Bath - Acid Stop - 00:30
    3.) Wash - Running water, 2 fill & dumps of tank
    4.) Bleach - Sodium dichromate bleach - 2:30
    5.) Wash - Fill and dump tank for about 5 minutes, until water is not orange.
    6.) Clear - Kodak Hypo Clear - Two minutes with inversion.
    7.) Re-Expose, 60 watt room light, 1:30.
    8.) Second developer - D-76 - 7:00 @ 68F
    9.) Stop, fix, wash as normal.
    7.) Wash - Running water, 2 fill & dumps of tank.


    I've done this with Tri-X, Plus-X and Efke KB-25. I always develop in 1:1 for the first developer with slightly reduced time, and use the normal time for the second developer.

    As to Tech Pan or Maco IR, I've heard that both can be reversal processed. I did a few frames of HIE and they came out nicely, so I know that IR film works. Almost EVERYTHING will reverse; I've done this even with X-Ray film, though the bleach did quite a job on the emulsion - which brings up my next point - some films may need to be hardened depending on the film and bleach that you use ...

    The procedure is actually pretty easy, so give it a try.

  9. #9

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    Potassium vs. Sodium Dichromate?

    I realize this is an old thread, but thought it worth a shot. I'm trying to make my own bleach for a vintage photobooth process. The bleach I usually buy premixed is often out of stock, or hard to get. The formula on the spec sheet is Sodium Dichromate 15-25% and Sulfuric Acid 10-15%. The paper is a direct positive roll paper that's only in the bleach bath for a few seconds... since it's an automated process. So, my question is, what is the difference, if any, between sodium & potassium dichromate? Will they yield the same results? Would I need a different quantitiy with potassium? Also, I can't seem to find a place to purchase Sodium Dichromate... However, Photographer's Formulary does sell Potassium Dichromate. FYI: Process for the paper is:

    1 Tank/Dip Water
    2 Tanks/Dips in developer @ 110-115 degrees. (Potassium Sulfite 25-35% & Hydroquinone 1-5%)
    2 Tanks/Dips in water.
    1 Tank/Dip in bleach: (Sodium Dichromate 15-25% and Sulfuric Acid 10-15%)
    2 Tanks/Dips water.
    2 Tanks Clearning Powder: Sodium Sulfite (100%)
    1 Tank/Dip Water
    1 Tank/Dip Toner: (Sodium Hydroxide 10-15% & Thiourea 3-5%)
    2 Tanks/Dips Water.

    Entire process is about 2.5-3 minutes, and generally yields nice strips...

    Any help would be much appreciated! Thanks!
    Best,
    -Ant

  10. #10
    cinejerk's Avatar
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    just wondering if results for the D76 formula above were ever published?

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