Purifying Ferric Oxalate

[karavelov]

Hello,

I am experimenting with silver-iron processes. I have some success with VDB but I want to try some POD process for better shadow separation. So I have decided to try making kallitypes. I have made the Ferric Oxalate following the procedure described here:

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The solution is green-brown and it has negative test for ferrous ions. But I suspect there is residual Oxalic Acid because mixing the sensitizer with 10% silver nitrate leaves white deposit on the bottom. The precipitation is slow and is accompanied with some gas emitted - I see little bubbles to form on the walls of bottle. I have also tried to neutralize the residual Oxalic Acid with adding more hydrogen peroxide but without success.

I have tried to make a kallitype print with it with some funky results - 5 minute exposure to the sun, developed in Sodium Acetate. The borders which had maximum exposure are solarized and turned brown, it seems it is a kind of POP process. The image is black but weak and blotchy.

Eric Nielsen also suggests that there should be further steps in order to use the Ferric Oxalate solution for kallitypes. He is referring to Dick Stevens' book for more details.

Could someone help my with this issue? How to get out the residual Oxalic Acid?

Thanks in advance

luben

 

[Dana Sullivan]

Unfortunately liquid grades of ferric oxalate are notoriously.... Bad. Precipitated ferric oxalate powder, though, has a very long shelf life once disolved into solution.

If you're interested in making your own powdered ferric oxalate, Jeff Mathias has a complete write up here:
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He uses paper towels to absorb the nitric acid from the precipitated ferric oxalate, but I would highly recommend the use of a buchner funnel and vacuum flask to remove the excess liquid.

Ignore Mathias' "tests" to determine the purity of the ferric oxalate, they are fictitious at best, libelous at worst. His assumption that solubility is strictly determined by the amount of oxalic acid in the solution is completely laughable. The fact that he lists the purity down to .01% should set off whistles and bells in your head...

 

[karavelov]

Thanks Dana,

I have read the Mathians' paper but it seems too much work and time consuming. I have no problem making small quantities of FO when I need it so the shelf life is not a problem. I have tested the produced FO with platinum and it works nice. I have also noticed that there is a some activity in the solution because there is some gas emitted - I think it is CO2 which is produced in the reaction of the oxalic acid and hydrogen peroxide. So I will wait another day or two and will test it again for residual OA. If there is still I will neutralize it with ferric nitrate (I have to buy some next week).

Thanks again and I will report my results

Best regards
luben