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  1. #1
    Murray Kelly's Avatar
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    Metol in glycol now horrible brown

    I thought to make up a concentrate of metol in ethylene glycol (propylene not available here, Australia) so followed the instructions from another thread with a slurry of glycol and metol with the TEA and small amt. of water all stirred together, with some small heat applied. Finally made up to volume with more e-glycol.
    Looked good for a week (pretty green - antifreeze) but gradually it's gone to coffee color over the month since I brewed it. I'd say it was dead.
    Anyone else had such an experience?
    I want to try various metol developers without going down the path of making larger quantities that will probably be never used again - a concentrate offers the freedom to try this and that without that drawback.
    Is ethylene (v. propylene) glycol unsuitable for a metol concentrate?
    Murray

  2. #2
    Nicholas Lindan's Avatar
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    What turns the metol brown is oxygen - assuming all the ingredients were good, then putting the glycol and TEA in a 300F oven for an hour and boiling the water for 10 minutes should drive off any dissolved gasses. Mix the metol into the cooled degassed liquid. You still need to keep the stuff in an air-tight/air-free container and away from bright light. Adding some sulfite after the metol has dissolved will help to preserve the metol. As metol is never used without sulfite (TTBOMK) the sulfite addition will not limit your use of the metol.

    I am not sure of the reason for doing this, metol keeps very well as a powder. If you want a liquid form you might just want to make up D-23 developer as a 'soup base', as it were: Add more sulfite, HQ & borax/boric acid to make D-76; add carbonate, HQ and bromide to make D-76; add pickling salt to make Microdol-X ... D-23 keeps for several years in well stoppered bottles if made with degassed distilled water.
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  3. #3
    Photo Engineer's Avatar
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    Murray;

    The extra components of EG in antifreeze can be the cause of part of the problem, as can be the addition of the water. The idea of many of these concentrates is to totally eliminate water. If water is present, you need some sulfite.

    PG is safer. EG is quite toxic. PG is widely used in the dairy industry and food industry.

    PE

  4. #4
    Murray Kelly's Avatar
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    I know that oxygen is the culprit.
    I was lead to believe that the concentrate was immune from this problem if prepared this way. The amount of water is minimal. Seems it is still too much.
    I'm not sure, but there is IIRC benzoate in there, too. As a denaturant? Will have to check the label again, tomorrow. Now 1am.
    I am aware of the oral toxicity of e-glycol. I promise not to drink it.
    The container is glass with a metal lid and a rubber sealing ring. Kept in the dark and cold.
    Wasn't thinking D-23, more your pyrocat etc or the Pyrocat-MC. No Sulfite.
    Didn't think of boiling the water. If there's no water, theoretically it shouldn't go 'off', but how to dissolve the metol without it?.
    Thanks. Off to bed.
    Murray

  5. #5

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    Well, Mr Gainer is the expert on this but my guess is that only enough water is needed to remove the sulfate from the metol:
    (C7H10NO)2.S04 +H2O -> H2SO4 + etc.
    For 344.38g metol 18g water would react thus.
    Don't take this as reliable, I never saw an expert give details of the reaction.

  6. #6
    Photo Engineer's Avatar
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    TEA will react with the sulfuric acid and TEA.Sulfate should dissolve in the EG. The Metol free base should then dissolve, but IDK. Not sure about the formula.

    PE

  7. #7

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    The usual reason for doing this with phenidone is to simplify measuring relatively small quantities of phenidone for developing just one or two rolls of film. A typical metol formula uses about ten times as much metol as a phenidone formula does of phenidone, so there's very little benefit to mixing up a solution of metol in glycol. For instance, a liter of full-strength D-76 uses 2.0g of metol, vs. 0.2g of phenidone in a liter of full-strength E-76. If you've got a scale that can measure with a precision of 0.1g, you'll get reasonably good consistency in your measurements of 2g of metol. Scales with a precision of 0.01g are fairly inexpensive (although the cheapest of these may not be very durable), so even if you wanted to mix up 250ml of 1/2-strength D-76, thus requiring 0.25g of metol, you could do it with pretty good repeatability of your metol measurement. This is the way I'd go, rather than mix metol in a glycol -- and particularly in automotive anti-freeze, which as PE says, contains other ingredients that might be detrimental to the keeping properties or to developers generally.

  8. #8
    gainer's Avatar
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    I don't remember why I proposed this, but it is used in the preparation of Pyrocat MC. I have several bottles of that dark brown sludge. Just for fun, try making a dose of D-23 to see if it really is dead. Many chemicals of its ilk are, IIRC, pretty strong dyes. I'll do the same here. You could also try Metol and ascorbic acid in 800 ml saturated borax solution brought up to 1 liter with plain water.
    Gadget Gainer

  9. #9
    gainer's Avatar
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    My little brown bottle did nothing but be brown. How enough oxygen could be trapped in that bottle to kill several grams of metol base, I do not know. Perhaps there is some other mechanism for self destruction. According to Sandy King, the Pyrocat MC has a good lifetime. It does have the ascorbic acid for preservative.
    Gadget Gainer

  10. #10
    Murray Kelly's Avatar
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    My thanks to all. Back to the drawing board?
    The reason I want to experiment with small quantities BTW is that I only need 100ml of developer to do a strip of 16mm microfilm from the Minoltas.
    I am looking for pictorial and phenidone has 'problems' such as uneven tonal gradation in seemingly even gray areas. It has to be dilute (not Beutler) and low pH.
    Murray

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