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  1. #1

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    Separating alkali from developing agents?

    Hi,

    A few possibly silly questions from a non-chemist to the chemists:

    For those who brew their own MQ developer, does it make sense to mix two separate baths, one that contains metol, sodium sulfite, hydroquinon (and possibly potassium bromide), and another that contains only the alkali, and then mix them just prior to development? Would the storage life and working characteristics of two separate baths be better/more consistent compared to a single bath?

    The reason Iím asking is, the Anchell&Troop cookbook claims that the activity of the published D76 formula that contains both metol and hydroquinone is variable over time due to a rise in alkalinity. Iím wondering whether separating the alkali as described above would prevent this problem?

    Iíve tried D76H (the version without hydroquinone) and found that it is visibly less active (thinner negs) than regular D76. Hence my desire to pursue the MQ combination.

    Also, is the variability in activity (due to PH change) of D76 pertinent to all MQ developers? E.g. Adox MQ Borax or Agfa/Ansco 17? Adox MQ Borax has 4g of Borax instead of 2g in D76. Would the larger borax content prevent a PH change during storage?

    It is the Beutler formula, where two separate baths mixed just prior to development, that made me think it could be adapted to all developers.

    Please note that Iím not talking about two bath development. Iíve tried that line and didnít find a visible advantage.

    Regards

  2. #2

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    What Anchell says is true but not a serious concern. People use D-76 in a replenished system for months without any problem. And yes it applies to low alkalinity MQ developers for film.

    D-76H should have the same activity as D-76. But it is intended to be used as a one shot and not replenished. Note that the Metol content is slightly higher than for regular D-76.

    The Beutler formulla can be made as a single solution if oxygen is excluded from the solution. Tetenal did this by supplying Neofin Blue in a sealed glass ampoule. This isn't really practical for the average user hence two solutions. A similar developer Ethol TEc was supplied as a single solution in an ordinary bottle However once opened its life was rather short.

    Everything considered dividimg a developer into parts really doesn't get you much. Kodak gives the shelf life of stock D-76 as 6 months. Always determine how much you mix based on how much you will use in this time period.
    Last edited by Gerald C Koch; 02-20-2013 at 03:03 PM. Click to view previous post history.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

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  3. #3
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    D76 is a marvellous developer and suggest you trust in the fact that the Kodak team, with combined chemical expertise, knowledge and experience know what they are doing.

    ďThe contemplation of things as they are, without error or confusion, without substitution or imposture, is in itself a nobler thing than a whole harvest of inventionĒ

    Francis Bacon

  4. #4

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    I don't think you will ever have a problem mixing developers as you suggest, i.e., making a stock solution A with everything minus the activator(s) and a stock solution B with the alkali (carbonate, metaborate, etc., etc.) and then combining the two just before developing. Many developers are formulated to be used exactly this way.

    Those that aren't aren't adversely affected by being mixed fresh just before use (except the possibility of undissolved particles...). The real question, I suppose, is whether dividing the stock solutions will get you any real increase in shelf life. That would have to be tested. As for eliminating the slight increase in activity of D-76 when it ages, this should do the job splendidly.

    Best,

    Doremus


    www.DoremusScudder.com

  5. #5

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    Hello,
    if you separate the development substance together wit sodiumsulfite from the alkali (Borax) you have nearly the formula of a D-76 2-bath developer. The life time of solution A is very long without the borax and is determined mainly by the carry out of a small volume with each film. The oxidation of hydroquinone and metol by air is faster at higher pH values. There are many formulations in the old literature based on stock solutions.

  6. #6

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    Sodium Bisulfite is known to be a preservative of metol (it's in part A PMK Pyro) and of hydroquinone (it's used in certain skin lightening creams for this purpose).
    So if the metol and hydroquinone was dissolved in sodium bisulfite solution to make part A and the other ingredients in part B in theory a long lasting two part D-76 looks possible to me.
    But AFAIK nobody ever did the calculations and experimentation that would be needed.

  7. #7

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    The acidity of sodium bisulfite would have to be taken into account.

    Considering the long shelf life of D-76 why are people trying to solve a non-existant problem. If you cannot use up a liter of developer in 6 months then why are you doing wet photography?
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  8. #8

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    Alan, I thought the preservative action of Sodium Bisulfite in most "part A" solutions was simply due to its acidity, which lowers the pH of the solution and therefore slows or inhibits oxidation of the developing agents (most developing agents, but especially ones like Pyrogallol which oxidize quickly in alkaline solutions). As I understand it the elegance of using Sodium Bisulfite for this purpose is it then converts to Sodium Sulfite when the alkali (usually Carbonate but Metaborate in the case of PMK) part B is added, which gives the working solution the required/desired amount of Sulfite.

    I wonder though if that mechanism would work with Borax or if the alkali needs to be stronger.

    On balance Gerald is probably right. Separating the alkali seems to be far more necessary in the case of acutance and/or Pyro developers where there is relatively little preservative, a low concentration of developing agent(s), and a relatively high pH. D-76 has none of these properties.

  9. #9

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    Basically it's because if you can make a liter of developer last 2 years you have a choice of 4 different, rather than one lasts 6 months.

  10. #10

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    Quote Originally Posted by Alan Johnson View Post
    Basically it's because if you can make a liter of developer last 2 years you have a choice of 4 different, rather than one lasts 6 months.
    OK but then the question becomes "If you cannot use up 4 liters of developer in 24 months then why are you doing wet photography?" (Before anyone jumps in, who has not read the complete thread, this thread is not discussing replenished systems.)

    The shelf life of D-23, which contains no added alkali like boxrax, is the same as that for D-76. So mixing up two solutions with the borax in one and the rest of the chemicals in the other doesn't provide any advantage.

    Forgive me but I don't see any real problem. Most people can mix up a batch of D-76 in less than 30 minutes. This includes the time to get the balance and chemicals off the shelf and cleanup afterwards. It's not rocket science. Just mix up what you think you will use in 6 months. Be that a liter or a gallon.
    Last edited by Gerald C Koch; 02-21-2013 at 12:56 PM. Click to view previous post history.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

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