Re: Potassium Oxalate

Hi Marek,

Thanks for your comments, and thanks to all the
others who responded today to my questions about
potassium oxalate and oxalic acid.

The potassium oxalate solution that I mixed is
about pH 5.4 and in printing works exactly like
the old solution that I have been using in terms
of speed, exposure scale and tone.

But what about long term storage of potassium
oxalate solutions? Does the pH change over time?
I ask because I have an old bottle of the stuff,
stored partially full in a glass bottle, and
when I checked it the pH was over 8. Is it to be
expected that the pH increases with time, and if
so, should this be of concern?

Sandy

>Sandy,
>By using your recipe you have a fair excess of oxalic acid (about 17%),
>which is not that soluble. You can add some more potassium carbonate (as I
>noted, 10 maybe even 15 grams) and still have about 5% excess oxalic acid.
>Typical POTA solution should be on the acidic side.
>By adding some sodium carbonate you have created mixture of potassium and
>sodium oxalate, with really a small amount of sodium, inconsequential for
>Pd development (that would be my guess, I have not tried that trick yet).
>Sodium oxalate is not very soluble, especially in cold solution. If you
>have added more then a few grams it might crystallize from the solution.
>Marek
>>
>> I separated the clear potassium oxalate solution
>> from the undissolved stuff at the bottom and put
>> it aside. I then added about 100 gs of water to
>> the undissolved junk and stirred. But it still
>> did not dissolve, so I then added some sodium
>> carbonate (by mistake since I meant to add
>> potassium carbonate). There was a lot of fizzing
>> and when it stopped everything was in solution.
>> But what do I have? Sodium Oxalate, or a mixture
>> of sodium and potassium oxalate?
>>
>>
>>
>> Sandy
>>
>>
>>
>>
>>>I used the anhydrous variety of potassium carbonate.
>>>
>>>Thanks for the information about concentration.
>>>I will add some water to the solution and see if
>>>the stuff at at bottom dissolves.
>>>
>>>Sandy
>>>
>>>
>>>
>>>>Sandy,
>>>>What form of potassium carbonate did you use? If it is anhydrous, then
>>>> you
>>>>are about right, you can still add another few grams of potassium
>>>>carbonate, say 10 grams. If you used hydrated potassium carbonate, then
>>>>your proportions are off. By my estimation your solution is about 1.0M.
>>>> I
>>>>don't find any benefits using solutions more concentrated then 0.9M (im
>>>> my
>>>>practice, pritning Pd), so you can add some water to it (50-100cc).
>>>>You should not have any undissolved stuff.
>>>>Marek Matusz
>>>>
>>>>> I mixed up a solution of potassium oxalate
>>>>> following directions provided by Nzé Christian. I
>>>>> added 130 gs of oxalic acid to 500 ml of water,
>>>>> mixed until dissolved, and then added 100 gs of
>>>>> potassium carbonate, and finished by adding
>>>>> another 15 gs of potassium carbonate, and finally
>>>>> I topped off the solution to one liter. Distilled
>>>>> water was used.
>>>>>
>>>>> The solution works fine for printing but there is
>>>>> still some junk at the bottom of the container
>>>>> that has not dissolved. What did I do wrong? Do I
>>>>> need to add more water, increase the temperature
>>>>> of the mix, or other?
>>>>>
>>>>> Sandy King
>>
>>
Received on Wed Sep 15 16:35:07 2004