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  1. #11

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    Ole,

    Right, of course, I wasn't thinking about the PO in ionic form in solution.

    That must mean that I don't have too much calcium in my water (even though it is city water from limestone spring/well sources, and is considered 'hard' by many people), as I don't see the problem in the prints at all.

    However, if it is not soluble, how would it form crystals on the surface of the print? That would imply that it was in solution before the paper dried, correct?

    It seems that the formation of the calcium oxalate might be in the first rinse or clearing bath after the PO, because any traces of free oxalates will disappear fairly quickly unless Mike is using oxalic acid as a clearing bath acid.

    Any chance EDTA might bind up the calcium so it cannot react with the oxalates? I believe that is the mechanism it uses with a variety of metals (in particular copper and iron).


    ---Michael
    www.mutmansky.com
    B&W photography in Silver, Palladium, and gum bichromate.

  2. #12
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    Quote Originally Posted by Michael Mutmansky
    Ole,

    Does it strip off the potassium, or does it need free oxalic acid to form?

    Do you know if any of the clearing bath solutions are better at removing this if it forms?


    ---Michael
    If you are getting a precipitate on your prints, You should try mixing your first clearing bath with distilled water and go directly into it from your developer. Does your clearing bath look milky or clear? (Not colorless but Clear) If you are getting solids in your first clearing bath, you should try an alternative clearing process.

    Eric

  3. #13

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    Ole,

    Thinking about it, I am getting some calcium oxalate, but it is in the form of a precipitate in the water wash after the developer (that is cloudy after a print or so, I normally use a fresh water bath for each print).

    However, I'm thinking that the calcium oxalate does not have the tendency to form structures large enough to be visibly crystal forms unless there is an extremely large amount of calcium in the wash water, because it appears to precipitate rapidly before it has the chance to collect into larger structures.

    I'm thinking that it is a good suggestion for Mike to explore with some distilled H2O in the first bath, but it doesn't seem that it is the most likely candidate for the crystal problem.

    It might also help if he reduces the PO concentration down to 20-25%, as that would also reduce the possibility if the oxalates are indeed forming a crystalline calcium oxalate.


    ---Michael
    www.mutmansky.com
    B&W photography in Silver, Palladium, and gum bichromate.

  4. #14
    Ole
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    Quote Originally Posted by Michael Mutmansky
    However, I'm thinking that the calcium oxalate does not have the tendency to form structures large enough to be visibly crystal forms unless there is an extremely large amount of calcium in the wash water, because it appears to precipitate rapidly before it has the chance to collect into larger structures.
    Oddly enough, the less calcium there is the larger crystals will tend to form. With lots of calcium it will just go milky with lots of microscopic grains...

    "Insoluble" is a relative term. Calcium oxalate is relatively insoluble, but still soluble enough that crystal growth will occur with low calcium concentration. Reducing the oxalate concentration enough to matter is not a viable proposition, you would have to go down to a few ppm to make any difference! It is much easier to eliminate the calcium.
    -- Ole Tjugen, Luddite Elitist
    Norway

  5. #15
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    There is no reason to dilute the developer to avoid the problem. He simply needs to avoid either a plain water rinse or use only distilled water. I use a reverse osmosis system and use it to rinse my prints after the developer and before the first clearing bath.

  6. #16

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    Eric,

    You missed my point, which was that a lower concentration PO solution will clear more quickly out of the paper, and will make it possible to possible get a fairly complete clearing of the PO in a single wash bath before moving to clearing baths. The less PO left, the less oxalate to react with any calcium in the clearing baths.

    It's also a good reason to encourage the physical removal of the PO by dumping; something that may not be stressed enough in the normal texts.


    ---Michael
    www.mutmansky.com
    B&W photography in Silver, Palladium, and gum bichromate.

  7. #17
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    Well the problem was that my developer was too hot(110). I confirmed this yesterday evening. With the new developer this started happening. When I backed down to about 90 degrees it stopped. I was trying to make my own PO and it ended up in a mess. I am no chemist. Thought I could save some bucks but ended up throwing good money away for bad. I'll not do that again. I was happy to find out that Mike at Artcraft will really discount the price when you buy five or more pounds of the powdered PO. That was good news. Everything is working fine now with lowering the developer temp. Now the new problem........................Has anyone ever noticed flucuations in UV output with a bank of BLB tubes? Are they sensitive to voltage flucuations? Thanks for all the good info guys I really appreciate it!!!!
    "EVERY film and paper is good .......... for something"
    Phil Davis

  8. #18
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    Michael, What do you mean " by dumping". I am not familar with that expression as used here. Do you mean, pouring off? I use a single tray method most of the time. So it all gets dumped off before clearing begins.

  9. #19
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    Quote Originally Posted by mikepry
    Well the problem was that my developer was too hot(110). I confirmed this yesterday evening. With the new developer this started happening. When I backed down to about 90 degrees it stopped. I was trying to make my own PO and it ended up in a mess. I am no chemist. Thought I could save some bucks but ended up throwing good money away for bad. I'll not do that again. I was happy to find out that Mike at Artcraft will really discount the price when you buy five or more pounds of the powdered PO. That was good news. Everything is working fine now with lowering the developer temp. Now the new problem........................Has anyone ever noticed flucuations in UV output with a bank of BLB tubes? Are they sensitive to voltage flucuations? Thanks for all the good info guys I really appreciate it!!!!
    Mike, It is really easy to make it yourself. 2 lbs of Potassium Carbonate, 1.75 lbs of Oxalic Acid and some water. Add the Potassium Carb to 1/2 gal of water and stir. Then , slowly add the oxalic acid in a well ventilated space, and you should end up with a about a gallon after you top it up. Did it bubble up to fast? I use a 3 gallon container when I mix a gallon. Keeps it all inside the bucket.

    Lights can vary in their output. If you have another wattage device on the circut, you may want to rearrange the plugs to better distribute the load. Poor grounding can also look like a voltage drop and cause your lights to flicker.

    Eric

  10. #20

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    I prepare my PO solution just as Eric describes and I have never had crystallization problems, but then again I nearly always use the PO solution at room temperature.

    However, if I understand the issues as they are being stated, I conclude the following. Please correct me if I am wrong.

    1. Michael proposes using a weaker solution of potassium oxalate because this apparently gives better clearing in his condition. I am assuming he mixes the PO solution from well water rather than with distilled water?

    2.Ole suggests that problems in clearing may be due to the formation of calcium oxalate, and proposes as the solution ether filtering the PO solution, or mixing it with distilled water, noting that reducing the concentrate of the PO solution will not address this particular problem.

    3. Eric uses a concentrated solution of PO, and mixes with a reverse osmosis system, and apparently gets good clearing with this technique.

    In my own work I usually have no problem at all in getting good clearing, with PO solution mixed with tap water, but have noticed that from time to time a fresh mixture of PO would immediately result in some staining, even though all other conditions were the same. From this discussion I am beginning to suspect that the culprit for this may be seasonal changes in my tap water so I will plan to mix my PO solutions in the future with distilled water.

    Now, is there any literature which suggests that the clearing baths might also benefit from being mixed with distilled water.


    Sandy


    Quote Originally Posted by EricNeilsen
    Mike, It is really easy to make it yourself. 2 lbs of Potassium Carbonate, 1.75 lbs of Oxalic Acid and some water. Add the Potassium Carb to 1/2 gal of water and stir. Then , slowly add the oxalic acid in a well ventilated space, and you should end up with a about a gallon after you top it up. Did it bubble up to fast? I use a 3 gallon container when I mix a gallon. Keeps it all inside the bucket.

    Lights can vary in their output. If you have another wattage device on the circut, you may want to rearrange the plugs to better distribute the load. Poor grounding can also look like a voltage drop and cause your lights to flicker.

    Eric

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