Ian;

There are several uses of Iron complexes with EDTA, but color photography is at the head of the list. Recently, with the introduction of NTA, the balance is shifting away from EDTA due to the higher BOD/COD of the latter and due to the "toxicity" of EDTA when in fact, EDTA is used intravenously in certain medical procedures (that being the secondary use of some of the complelxes).

So, it is a rare beast just for color photography and it promises to get rarer and more expensive.

Here is a scheme for making your own Ammonium Ferric EDTA. It should work. I have not made this in the lab for over 30 years though, so I'm writing this from old memory.

Start with EDTA (the acid itself). Dissolve slowly in concentrated Ammonia solution (28%) until this is neutral and then add an equal molar (to the EDTA) quantity of Ferric Chloride. This will make a concentrate of Ammonium Ferric EDTA and Sodium Chloride in equal molar concentration. The pH should be about 6.5, never higher, and never lower than 4.0.

If you go over about 6.5, you will precipitate Ferric Hydroxide which ruins the mixture and if you go below 4.0, the Ferric Ammonium EDTA will precipitate out. You will then have to make it alkaline and the dilution will decrease the strength of the concentrate.

After you are done, add 1% excess of EDTA acid and readjust the pH. This last step is absolutely critical. If you omit it, you will cause severe stain in your photos. Iron salts will precipitate out in the film or paper and cannot!!!! be removed under normal circumstances.

PE