Ferric Oxalate

[Jorge]

Anybody has any idea why I am having so much trouble dissolving Ferric Oxalte? I bought a new bottle from B&S about a month ago, the first time I made a batch it went great, but now I have tried 4 times and it wont dissolve. I called B&S and Keving Sullivan was really nice and promised to replace the powder, but I am still concerned as to why this happened.

I did manage to dissolve it after about 1 hour and at very high temperatures, but I did the ferricyanide test and it showed ferrous oxalate present, no doubt because of all the stirring and heating the ferric oxidized. So that went down the drain.

Any things I should be looking for? does the addition of oxalic acid make any difference? should I skip adding oxalic acid? maybe oxalic acid lowers the solubility constant, but as I said I had no problem with my first batch even adding the oxalic acid.

Thanks!

 

[carlweese]

I've been using ferric oxalate powder from ArtCraft Chemical for a couple years now. It is very pure and hard to dissolve unless doctored slightly. I measure 15 grams of the pure FO, then add two grams of oxalic acid, then one gram of EDTA tetra. Funnel into a 100ml capacity brown bottle. Add 55ml of distilled water, then alternate ten second blasts in a microwave oven followed by vigorous shaking. In tests, I found I could never get it to dissolve without the additives, no matter how much it was heated, but with the additives it suddenly goes into clear state at a hot but well below boiling temperature. I suspect that the purity and amount of either impurities or intentional additives will change the ease with which FO powder dissolves. Using the above technique, I get liquid FO that has excellent shelf life (at least 4-6 months, though I seldom have it around that long) and complete consistency from one mixed batch to another--one time when I'd mixed up a new batch I made comparison prints with the dregs of a months-old bottle, and the prints were identical.

 

[Jorge]

Thank you Carl, I have a couple of questions, how reliable is the ferricyanide test? and I notice you use more OA than normal, is there any reason for this? better keeping qualities?
I tried the EDTA trick as suggested by Kevin and still could not get it going. I use a combination hot plate stirrer so I dont think the temp and agitation are my problems.
I was confused since my first batch went without a hitch, must have been beguinners luck, but since you also experience this I guess is normal.

 

[clay]

Jorge:

I have had the same problem occasionally with B&S FO. I use hot distilled water (about 140 degrees or so) and then shake vigorously and let it sit overnight. Then I shake again for about 2-3 minutes and let it sit another couple of hours. If all else fails, then I add very tiny amounts of water and pinches of oxalic until it all dissolves. Normally the extra water will do the trick. Needless to say, I plan ahead of actual need!

I can also vouch for the artcraft FO. I mixed up a batch just as Carl described, and the resulting prints were indistinguishable from B&S derived prints.

Shake it!

Clay

 

[Jorge]

Carl and Clay, another question/observation. I received an e mail from Kevin telling me I must add the OA after dissolving the FO. I had done that with my first batch and for the following ones I did the same thing, funny things was in these later tries as soon as I added the OA the FO went out of solution and back into a slurry....what gives?
The other thing Kevin mentioned to me was that the ferri test was not very reliable, that I should do a silver nitrate test, what is this test? I cannot find any info on this. Thanks.....

 

[carlweese]

Since getting the ferric into solution is the main reason to add the oxalic, the first advice doesn't seem to make sense. Also, I have not heard from other sources that the ferri test was "unreliable" but I don't know the chemistry. I think there's a treatment of the testing procedure on Jeffrey Mathias' web site Pt printing guide: Dead Link Removed

Don't know about a nitrate test, never heard of one, but the chemistry is not my end of things.---Carl

 

[Jorge]

Thanks Carl, this is why I like to double chek things. The test in the Mathias site is the one I was reffering since it is the one I use.
Ah heck I guess this is one of those misteries that drove them crazy 100 years ago.....thank God for the internet and APUG, and of course you guys.

 

[b.e.wilson]

Knowing nothing of the Pt/Pd process, but knowing chemistry, I suppose there isn't a possiblility of substituting ferric citrate for ferric oxalate as the sensitizer? Ferric citrate is stable, and citrate, like oxalate, is a reducing agent. Ferric citrate, however, is not light sensitive, and perhaps that is why it is used.

 

[avandesande]

How about adding ferric cloride, oxalic acid, and sodium carbonate together? I think i have seen formulas for making your own on the web. Ferric cloride you can get at electronics stores,(echant), oxalic acid is sold at pep boys as radiator cleaner, and you can get sodium carbonate from the food store (washing soda).
--Aaron

 

[Jorge]

Bruce you got it, ferric citrate is not light sensitive thus not of much help.
Aaron thanks for the idea, yes there are ways to make the stuff yourself, but for the cost and obtained purity is worth it to just buy it done. At least in my case.

 

[avandesande]

Solutions of these three items should last indefinitly, and I bet once you worked out the process, it would take less time to mix them than to dissolve the solid. Also, the solid ferric oxalate has a finite shelf life and a dubious purity, I am guessing that the fresh mixed stuff would be significantly purer than the redissolved solid. It's not cheap either.

--Aaron

 

[Jorge]

Making FO is a little bit more involved judging from the literature I have seen, for example the B&S method uses ferric ammonium sulfate to which you add ammonium hydroxide, to the resulting product you add oxalic acid to make ferric oxalate:

Fe(NH4)(SO4)2+3NH4OH-----> Fe(OH)3+2(NH4)2(SO4)

2Fe(OH)3+3H2C2O4 (H2O)2---------->Fe2(C2O4)3(H2O)6 +6H2O

Simple, but as you see the components are not that easy to get, specially here in Mx.
I have seen other methods where they add Ferrous ammonium sulfate to OA and then Hydrogen peroxide to oxidize the iron to ferric, but again, you have heat generation and efervecense, not really something I want to do in the darkroom.
The most dangerous I have seen was adding Ferric Nitrate to OA to make Ferric Oxalate and nitric acid, not something I want to do at home!

Your idea might have merit, using Ferric chloride and OA, wich would yield OA and Hydrochloric acid and the sodium bicarbonate as a buffer, I suppose if I check enthalpy tables I could see if the reaction proceeds, but as you can see this is becoming more and more involved and for me it is easier to just buy it new. Specially with the customer service B&S is providing, when I called them not only was Kevin Sullivan very helpful but offered to send me a new bottle free of charge!
FO is actually very stable, in the sense that it lasts years if kept closed tight and at normal humidities.
I know Terry King usually teaches in his workshop how to make FO, but I think this is one of those cases where conveninence outweights making it.
Thanks for your input and of course if one day you do decide to make pt/pd prints and make your own FO let me know how it went.