Potassium Bromide -- prevents developer oxidation?

Discussion in 'B&W: Film, Paper, Chemistry' started by Trask, Feb 17, 2009.

  1. Trask

    Trask Subscriber

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    I've mixed up (according to an older formula) a developer using Metol, HQ, sodium carbonate, sodium sulphite, borax and potassium bromide. A couple of liters. Then, per instructions, I mixed up a liter of replenisher, which is the same formulat minus the potassium bromide (because in use the re-used main developer will pick up bromide from the developing process).

    Interestingly, the two liters of primary developer are still quite clear, i.e, not brownish, after about three months and repeated use. The replenisher, mixed at the same time, is now relatively brown which indicates oxidation AFAIK. Each is in a fully stoppered bottle, and each bottle does have some air in it, relatively equal amounts relative to the surface area of liquid exposed. Air tight, light tight. Same storage conditions.

    So -- should I conclude that potassium bromide in a formula inhibits oxidation? Secondarily, do you think the brownish replenisher can still be used or should I toss it and mix up fresh? I usually take 30ml out of the main developer and add in 30ml of the replenisher for each roll or two run through.

    All thoughts welcome!
     
  2. Ian Grant

    Ian Grant Subscriber

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    No bromide won't inhibit oxidation. Sulphite and Metabisulphite are used to prevent oxidation. It may be differences between the storage bottles.

    You might be better off making up fresh replenisher , it's difficult knowing how far it's oxidised. When I made up my own re-plenishable devs like ID-11, ID-68 and Adox Borax MQ the replenisher lalways asted well with no bromide, so you need to look at why it's oxidised. Some plastics allow very slow diffusion of oxygen through the plastic wall and I did have Pyrocat HD which didn't keep well in small clear plastic bottles I stored it in, less than 6 months, but in good bottles it's still OK after 18 months.

    Ian
     
  3. OP
    OP
    Trask

    Trask Subscriber

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    Thanks, Ian. The bottles are identical -- same company, same material, same wall thickness, same caps. One is just bigger, but then it has twice as much solution in it. I appreciate your confirmation that it's not the presence or lack of potassium bromide. Perhaps the distilled water I used for each formula had differing levels of oxygen...
     
  4. Nicholas Lindan

    Nicholas Lindan Advertiser Advertiser

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    No, it doesn't. The sodium sulfite is the anti-oxidant in developer - the sulfite oxidizes before the metol or HQ. The sulfite also has a fine-grain solvent action.

    Bromide is not included in the replenisher formula because film development produces bromide all on its own. The action of development is to turn silver bromide crystals into metalic silver, the bromide so produced builds up in the developer. Diluting the built up bromide with bromideless replenisher is one of the reasons for drawing off a little liquid with each replenishment.
     
  5. dancqu

    dancqu Member

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    All things being equal there is less surface area relative
    to volume the larger the container. Also, minute amounts
    of some soluble materials can produce a great amount
    of color.

    The developer has been used while the replenisher has
    been taped but not used. Ordinarily one would think
    the used solution to be colored. An interesting
    observation. Dan