What colour is your Ferric Oxalate for Kallitypes?

[davido]

Greetings,

I've been struggling with the kallitype process off and on for a while now. I have yet to produce a print with real paper whites. I have tried pretty much everything from different types of paper and sensitizer application, 50% humidity during coating, one tray processing, different developers and temperatures, distilled water right after developer, using a ph meter, ect.

I have come across something which may or may not relate to my issue, but it seems worthwhile to mention, especially to those who are Kallitypists out there.

The dry ferric oxalate I've been purchasing from Bostick & Sullivan mixes up fine (eventually) - it's colour is a light lime green.
From my understanding the green comes from oxalic acid - the greener it is, the more oxalic acid.
This apparently can causes problems with the Kallitype process. I found this on a B&S article on their site:

" if one wishes to use [ ferric oxalate containing free oxalic acid] for Kallitype printing where the free oxalic will form an insoluble silver oxalate [Ag2C2O4], sludge that will interfere with the Kallitype process."

They then go on to say that they no longer produce ferric oxalate with free oxalic acid. I'm confused as to why their product is still green and not yellow?

Lukas Werth has suggested (in a few threads on APUG alternative), that " A yellow FO solution is what you want for kallitypes" and that " For kallitypes on the other hand, you want the amber colour, for the acid - presumably also other additions - causes the silver nitrate to precipitate."

I'm guessing that the vast majority of B&S ferric oxalate is sold to those using it for platinum printing, for which the oxalic acid is not an issue. But for Kallitypes it appears to be, so perhaps kallitypists are just out of luck?

So, where does one find a yellow or amber coloured ferric oxalate? And could the apparent oxalic acid , in the powder I've been purchasing, be related in any way to the staining I am experiencing?

David

 

[Ian Leake]

I thought B&S sold a ferric oxalate designed for kaloitypes (‘though I could be wrong).

You can add a tiny amount of ferric nitrate to convert the free oxalate into ferric oxalate. When the solution turns golden yellow the free oxalate has gone. This is easier said than done because you need to do it in the dark...

Alternatively you can make your own ferric oxalate, which is not that difficult.

 

[nmp]

I wonder if you could use CaCO3 (chalk) to neutralize oxalic acid into Ca oxalate which is insoluble. Both excess CaCO3 and Ca oxalate can then be filtered out.

 

[davido]

Thank you Ian and Niranjan for your responses.

Ian, B&S do sell ferric oxalate for Kalllitypes, however it is in liquid form - mixed at 20% instead of the 27% mix (which is used for Platinum Printing). I assume that the percentage is the only difference.
I have bought the liquid form in the past but it's not worth it with the shelf life being less than 6 months (B&S say it's 1-2 years but I think it's much less - probably more like 3-4 months). You also don't know when it was actually made by B&S?
I might try actually making Ferric Oxalate, though I'm a little apprehensive , but you say that it's not that difficult?

Niranjan, I'm not sure I actually follow your suggestion as I'm not a chemist. But I'm going to research your idea further. Thanks.

David

 

[Herzeleid]

Niranjan's ideas was quite appealing so I have tested it

Initially you will hear fizzing and small bubbling, it shows that excess oxalic acid is neutralized. My solution was quite yellowish in color but it turned amber.
Calcium carbonate has extremely low solubility in water but quite tiny bit dissolves and I believe it starts a double replacement reaction and ph starts to change.
And you end up with a murky solution, some iron carbonates or other oxides form. If you start adding drops of oxalic acid you can convert these oxides back to ferric oxalate.
It is possible to make it work but looks like it is tricky, not a straight forward simple solution.

Another thing that comes to my mind, since you have problems clearing the whites. Have you tried adding drops of hydrogen peroxide to your ferric oxalate solution?
Hydrogen peroxide will oxidize ferrous oxalate to ferric oxalate, preferably you might need a strong hydrogen peroxide solution. Let's say %50 solution, 1-2 drops should oxidize ferrous salts.
Or adding some dichromate to the developer solution will oxidize ferrous salts trapped in fiber and would help clearing, but it also increases contrast.

I have done a few batches of ferric oxalate (from various iron sources) in order to make ammonium ferric oxalate. I always had some problems with kallitypes, so I gave up on the process.

 

[Andrew O'Neill]

Mine is very pale green... from B&S.