Differences between Ferric Oxalate III and Ferric Ammonium Oxalate III

in kallitype making (and Pt/Pd chemistry as well) it is used Ferric Oxalate (or Iron III oxalate) powder

Mike Ware for the New Cyanotype forumla adpots Ferric Ammonium Oxalate III

Whate are the differences between those two chemicals? I found some data about the Ferric Ammonium Oxalate III and nothing about Ferric Oxalate III. Are they the same? What's their chemical formula and CAS number?

Ferric oxalate and ferric ammonium oxalate are different: generally, FO is used in develop-out processes, and FAO in print-out processes, though this is not always the case. You get FAO, but it is difficult to locate FO in Europe, as this chemical is, as far as I know, not widely used. You probably have to order it from the USA, or, as I do, get iron II oxalate (ferrous oxalate) powder which you can turn easily into the wanted iron III oxalate by mixing the as such insoluble powder in water with oxalic acid, and add hydrogene peroxide in drops to start the reaction. When you get an amber coloured fluid there is no or little free oxalic acid present, when the fluid is green there is. You will have to test for whether some ferrous is left by giving a drop into a weak ferricyanide solution: it must not become blue. This process is certainly not more difficult than getting FO (III) into solution.

thanks for the explanation, Lukas

Hi Fulvio,

I recently tried making kallitypes with Ferric Ammonium Oxalate. At first i had reasonable results but afterwards i was disappointed with them. I recently discussed this on the forum - you can find the discussion at (there was a url link here which no longer exists).