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  1. #11

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    Hello,

    I heard of a similar process where instead of a silver halide solvent in the developer a pre-exposure of the film is used. The density created by the pre-exposure will then be bleached away before the second developer. Does anybody here have experience with this?

    I want to use the process for enlarging 35mm negetives for gum-bichromate printing. Up till now I've used internegatives but this way it is very difficult to get clean results.

    Albert

  2. #12

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    Quote Originally Posted by eumenius
    Hello friends,

    I find bichromate bleach to be stable almost forever, and making no black mud on everything it touches - quite unlike the permanganate-based bleach. [...] after all, we wash our flasks with a saturated bichromate solution in concentrated sulfuric acid! Also, bichromate hardens the emulsion nicely, minimizing the risk of friction damage during treatment.

    Cheers,
    Zhenya
    First and foremost: the permanganate doesn't leave any residue, neither a black mud. What's this black mud?
    Is it the dissolved gelatine? If it is then you're probably using too much concentrated solution or too long time for it.
    I can say for sure (because I've spend so many hours doing tests) that the permanganate leaves no residues at all (as MnO2) if you use distilled water for all steps.

    The other thing: you say that you're a chemist. Then you should know that using the dichromate for cleaning up the lab glassware is an habit of almost 20/30 years ago and it's completely abandoned nowadays, because now it's used the ammonium persulfate with concentrated sulfuric acid (H.M.Stahr, L.Sigler, Anal. Chem., 54, 1456A, 1982).

  3. #13

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    Hi Alessandro,

    the manganese dioxide still forms somehow on the reels etc., with concentrations as indicated by Ilford, and I just don't like the permanganate as a matter of fact The orange color is better for me, at least the bichromate bleach allows for better visual control of my films. I can't advise anyone against permanganate, I just use whatever bleach I find more convenient Also I like the results, maybe that's my own opinion, but there you are - the permanganate bleach didn't give to me what I wanted, at least in my eyes.

    The sulfuric acid - bichromate mix is as old as Universe, of course, but it works fine - especially when the chromium ions adsorbed by glass are rinsed out with EDTA solution after cleaning, before the final wash. It also work well when hot. Maybe in some countries the method is abandoned now, yes, but we in Russia like and use it - because, for example, the working solution keeps OK for months, and we change it when it turns green. The persulfate baths should be prepared right before use, of course, and it's a big wastage of H2SO4, too - we already feel guilty enough about our environment. The persulfate itself is expensive and has a limited shelf life, and we got large drums of bichromate in stock. So, I can't see any reason to switch to alkaline permanganate, or persulfuric acid - the bichromate stuff, chrompick as it's called here, works fine and burns the most nasty dirt from our glassware.

    Regards,
    Zhenya

    Quote Originally Posted by Alessandro Serrao
    First and foremost: the permanganate doesn't leave any residue, neither a black mud. What's this black mud?

    The other thing: you say that you're a chemist. Then you should know that using the dichromate for cleaning up the lab glassware is an habit of almost 20/30 years ago and it's completely abandoned nowadays, because now it's used the ammonium persulfate with concentrated sulfuric acid (H.M.Stahr, L.Sigler, Anal. Chem., 54, 1456A, 1982).

  4. #14

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    Eumenius: I know many lab around the world still use the chromic acid. I wanted only to point out that there are alternatives methods (which have their pros and cons) available.
    I just feel that the extra risk is not worth the candle. In my lab we use alternatives methods and we feel much better this way.
    It's just my p.o.v.

    Good work.

  5. #15

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    Alessandro,

    the alternative methods of labware cleaning are good while they are not coupled with big expenses That's the question of a scientific school we'be been raised in - I just can't imagine my lab without chromic acid The risk of simple work in organic chemistry / biochemistry lab is much higher compared to bichromate risk, so it's okay for me. Why, I am working daily with highly radioactive iodine, and it's volatile - the bichromate does not fume, at least

    Good work too,
    Zhenya

    Quote Originally Posted by Alessandro Serrao
    Eumenius: I know many lab around the world still use the chromic acid. I wanted only to point out that there are alternatives methods (which have their pros and cons) available.
    I just feel that the extra risk is not worth the candle. In my lab we use alternatives methods and we feel much better this way.
    It's just my p.o.v.

    Good work.

  6. #16

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    The nuances of bench/lab practices escape me. On the other hand, your reversal protocol, Zhenya, promises all kinds of interesting revelations. What would those protocols be, exactly?

  7. #17
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    Me too I'm waiting the revelations !
    Actually I try to reverse differents films in a personnal process, it could be very interesting to compare the results and the process .


  8. #18

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    Quote Originally Posted by Kobin
    The nuances of bench/lab practices escape me. On the other hand, your reversal protocol, Zhenya, promises all kinds of interesting revelations. What would those protocols be, exactly?
    He-he, that's what I forgot to write, being lured out by the newest approaches in lab work

    So, I take Fomapan 100 in sheet size. It's a good film for reversal, because it's not made on blue Roentgen film base. The slightly matted backside doesn't make any troubles, either. Expose it as ASA 100 with daylight, ASA 90 with halogen light.

    The whole process I perform in trays - it's easier and safer, and I don't have any tanks for sheet film The temperature is one of your room, 20-22 Celsius. I can't say that the temperature is critical for the process - keep your 1st developer at 20-22 degrees, and it's okay.

    1. First development - 5 minutes

    Ilford P-Q Universal 1+5, with 10 g of hypo per liter. A constant agitation in first 30 sec, and 15 sec each minute. I find hypo to be a good halide solvent for the purpose, not worse than K thiocyanate - so I use hypo, because I just don't like KSCN

    I use my own-mixed P-Q:

    Sodium sulphite, anh. - 100 g
    Potassium carbonate, anh. - 100 g
    Hydroquinone - 31 g
    Phenidone - 1.28 g
    Potassium bromide - 5 g
    Sodium hydroxide - 2 g
    Water to 1 l.

    Add hypo right before using the developer, as it doesn't keep. 100 ml is sufficient for 6 9x12 or 4x5 sheets.

    2. Running tap water wash - 30 sec

    3. Bleach - until your black image dissolves completely, maybe 45 sec

    ORWO bichromate bleach:

    Potassium bichromate - 10 g
    Sulfuric acid, conc. - 10 ml
    Water to 1 l.

    Dissolve the salt first, and carefully pour in the acid, mixing well. Be careful with this solution, it can be harmful to eyes and skin. I don't touch it with fingers - in the dark I slide in the film to tray, move it a bit in and switch on a light on another table. At this time you should see your image and decide if it's worth of further processing Some experience will give you the feeling of right exposure. After all, the BW slide can always be reduced or intensified

    4. Running tap water wash - 30 sec.

    Take the film from bleach not by hand, please.

    5. Clearing and re-exposure

    Clearing bath:

    Potassium metabisulfite - 25 g, water to 1 l.
    Or sodium sulphite - 50 g, water to 1 l.

    Take your tray with clearing bath and film in it under your table lamp, with 100W opal bulb in it. Switch the lamp on and expose your film under it (~30-40 cm distance) for 30 sec each side. Move the tray about to give even light to it. The image becomes creamy-yellow, not white, in this bath.

    6. Running tap water wash - 30 sec.

    7. Second development.

    Ilford P-Q universal 1+9, without hypo (!!) - 5-7 minutes, longer time will do no harm either. The slides would appear "dark", but that's how they should be, don't worry.

    8. Running tap water wash - 30 sec.

    9. Fixer

    Your common fixer, 3 minutes. Just to be sure.

    10. Running tap water wash - 30 sec.

    11. If you wish, immerse your slides in a selenium toner solution to give them more permanence, for 2 minutes.

    12. Wash 10 minutes, treat with something like Ilford Ilfotol, hang to dry.

    This should work fine, giving you the real beauty

    If there's any questions regarding the process, ask me and I'll write more - that's just a preliminary but fully working protocol.

    Cheers from Moscow,
    Zhenya
    Last edited by eumenius; 11-11-2005 at 10:32 AM. Click to view previous post history.

  9. #19

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    Thanks, Zhenya.

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