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  1. #11
    smieglitz's Avatar
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    Quote Originally Posted by eumenius
    ...It's almost like my dream about cesium astatide ...
    Zhenya
    Hmmm? Guess you had to be there.

    Joe

  2. #12

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    The potassium iodide itself keeps well in the dark and when dry - but I found some older preparations from our lab shelves (likely from 60s) to be quite yellow, and to possess the smell of iodine. Maybe something from the packaging or from outside spoiled them, that doesn't seem to be a spontaneous decomposition. Iodides of alkaline metals seem to be light-sensitive too, like silver iodide - but to a much much smaller degree.

    Quote Originally Posted by gainer
    Correct me is I'm wrong (do I have to ask?) but I have seen potassium iodide on my druggist's shelf without any statement of limites shelf life.

  3. #13

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    I apologise for rehashing this old discussion, but I'd like to know, would making a 10% solution of KI be problematic in terms of solubility and longevity?

    I ask this because I have a 10g sachet of KI, but my scale is only precise to 1.0g. I was thinking that I could dissolve 10g of it in 100ml of water, and derive less concentrate solutions from that.

    If anyone's curious, I'm trying to mix up some FX-1, which calls for a minute amount of KI. I think the 10g will last me 'quite' a long time.

    Thanks in advance!

    Justin

  4. #14
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    Justin, KI (Potassium Iodide) as stated here is not completely stable in solution and will decompose. Your 10% solution is easy to mix, but will probably go bad within a year unless kept refrigerated.

    Even then, a years keeping might be chancy but I'm not sure, never having tested it out. I refrigerate mine and keep it for about 6 months, then mix fresh.

    PE

  5. #15

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    Quote Originally Posted by Photo Engineer
    Justin, KI (Potassium Iodide) as stated here is not completely stable in solution and will decompose. Your 10% solution is easy to mix, but will probably go bad within a year unless kept refrigerated.

    Even then, a years keeping might be chancy but I'm not sure, never having tested it out. I refrigerate mine and keep it for about 6 months, then mix fresh.

    PE
    PE, thanks for the information. I guess I should look for a more precise scale.

  6. #16

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    For over 25 years starting 1962 the formula of FX-1 was published in BJP annual and referring to the 0.001% solution of potassium iodide the copies I have said "this keeps for 2 years at least".It is suggested to dissolve 1g in 1000ml water,dilute 100ml to 1000ml,then 100ml to 1000ml again to get a 0.001% solution.

  7. #17

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    A small amount? Yes, I would say that 5ml per liter of working solution of a 0.001% solution is indeed a small amount.

    Wonder why so little. I have experimented with potassium iodide in several formlas and it takes much, much more than that to have any anti-fogging qualities. But perhaps anti-fogging is not its purpose in FX-1?

    Sandy

    Quote Originally Posted by Justin Low
    IIf anyone's curious, I'm trying to mix up some FX-1, which calls for a minute amount of KI. I think the 10g will last me 'quite' a long time.

    Justin

  8. #18

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    Originally (BJP Jan6 1961) G.W.Crawley wrote to the effect that the micro concentration of potassium iodide probably worked with some but not all films of that time by shortening the inductance period and "setting" fine surface detail early on.The effect of similar concentrations of oxidation products had been known for some time.The iodide ion may enfeeble the developing agency and predispose it to produce adjacency effects.Eberhard effects only form in a weak developer,metol<0.5g/L ,sulfite<6g/L.
    If this still is the case with modern films appears not to have been commented on.

  9. #19

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    As a footnote to this,I wrote to Geoffrey Crawley to ask if the very small amount of potassium iodide in FX-1 produces edge effects with modern films. He replied (Amateur Photographer Apr 1 06) to the effect that" There is indeed no point in adding the iodide to FX-1 with modern films" FX-1 was designed for the era of "acutance "films.It remains a valid tool for processing slow and medium speed films but if some ,like T-max 100 ,give results which are a little flat,25mg potassium bromide can be added per working litre.
    FX-2 now seems to be the preferred high definition developer for modern films,he noted.

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