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  1. #21

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    Quote Originally Posted by Gerald Koch
    Alessandro,

    What are the instructions for the Tetenal Hardener? Are you using it correctly? If they say to add it to a plain hypo solution then you are not following the directions.
    The label on the Tetenal hardener bottle says: "Harder for fixing bath, diluite 25ml/l of fixer" and that's all.
    It doesn't refer to what type of fixer should be.


    Quote Originally Posted by Gerald Koch
    What you are starting with is a non hardening FIXER which already contains, besides thiosulfate, sodium sulfite and sodium metabisulfite. For example, if you would look up the formula for Kodak F-5a Hardener you would see that it says to add the hardener to a 30% solution of sodium thiosulfate. No mention of added metabisulfite or sulfite.
    Yes but it would be the same: the sulfite is contained in the hardener this time.

    Dunno wheter the same amount of sulfite is contained in the Tetenal hardener, I have to look at the Tetenal MSDS, but unfortunately it seems I can't find them.


    Quote Originally Posted by Gerald Koch
    Film intended for reversal is usually shot at an EI above the manufacturer's rated speed. If you fail to do this the slides will be very dark.
    Isn't just the opposite? If I expose the T-Max 100 1 stop lower (@50) I'll get brighter slides. The opposite if I rate the film @100 or 1 stop higher. Isn't that way?


    Quote Originally Posted by Gerald Koch
    As far as using potassium dichromate this is safe to use, as are all commonly used photochemicals, if some care is observed. I certainly consider it safer than pyrogallol and catechol which are in common use as developing agents.
    Jerry
    I agree on the catechol, not on the pyro. The pyro is way less toxic than dichromate (as you can see from any MSDS).

    Thanks for the useful infos.

  2. #22

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    Quote Originally Posted by Alessandro Serrao
    Isn't just the opposite? If I expose the T-Max 100 1 stop lower (@50) I'll get brighter slides. The opposite if I rate the film @100 or 1 stop higher. Isn't that way?
    You're right. Since I never do B&W I always get this backwards.

  3. #23

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    Quote Originally Posted by Gerald Koch
    [...]Since I never do B&W[...]

  4. #24
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    Quote Originally Posted by Alessandro Serrao
    For what I've understood, low pH causes the precipitation of the colloidal sulfur. I'm guessing this was the case.
    Sulfuring of fixer, I've read, is caused by oxidation, not by low pH. High (alkaline) pH, OTOH, can/will cause precipitation of an alum based hardener. And that's the number one thing -- alum hardeners can *only* be used in an acidic fixer, not in neutral or alkaline fixers. The presence of acetic acid in the hardener may be insufficient to prevent precipitation when diluted out in either water or the near-neutral fixer formula you gave earlier. Try adding acetic acid, to at least half the strenth of acid stop bath working solution, and see if that stops the precipitation.

    Or consider changing to a non-alum hardener, which you could even apply before the first dev. The bad news is, most if not all non-alum hardeners use an aldehyde (formalin is common, but glutaraldehyde is also used) and there are some significant health risks in using these in a closed darkroom. Even those that, like Kodak's C-41 stabilizer, don't include formaldehyde in the list of ingredients contain ingredients that react to produce the stuff.

    Here's a potentially simple way to test if your precipitate is alum or sulfur: intentionally produce some and filter it out (a paper coffee filter should work, if you don't have chemical filter paper available). If it's sulfur, once the precipitate is dry it'll be yellow-white, possibly with brown and red streaks or mottling caused by particle size, and will smell strongly of sulfur oxides even at room temperature; only carbon disulfide will dissolve it, a sample will burn with a faint blue flame and smell strongly of sulfur dioxide, and heating a tiny sample with candle wax will give off hydrogen sulfide (do this outdoors -- it takes frighteningly little H2S to kill you). The alum precipitate, OTOH, will likely redissolve in acetic acid in the stop bath strength range, won't ignite at all, and won't react with candle wax in a way that gives a strong odor.

    Once you know which precipitate you're getting, you'll be ahead of where you are now.
    Photography has always fascinated me -- as a child, simply for the magic of capturing an image onto glossy paper with a little box, but as an adult because of the unique juxtaposition of science and art -- the physics of optics, the mechanics of the camera, the chemistry of film and developer, alongside the art in seeing, composing, exposing, processing and printing.

  5. #25

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    Quote Originally Posted by Alessandro Serrao
    Sorry I meant to say B&W reversal processing. The main problem today is finding a suitable film with a colorless base.

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