[alt-photo] Fluka / Sigma-Adrich Ammonium Iron(III) Citrate - contains Fe(II)!!!

[Loris Medici]

Hi all,

I've just purchased Ammonium Iron(III) Citrate from Fluka / Sigma-Adrich. (See product info here: http://bit.ly/9nrgtj, Lot #BCBB2047)

Unfortunately, as soon as I mix stock soln. A and B ,I get spontaneous blue in the the cyanotype coating solution. I think this is indication of some Iron(II) impurity!!! (It's not the ferricyanide, that works w/o problems with B&S AFC...)

I tried to add small amnt. of OTC 3% hydrogen peroxide in soln. A, in order to convert Iron(II) to Iron(III) and it worked. (Two drops of peroxide in 10 drops of 25% AFC cures the instantaneous blue problem completely...)

So,

1. Beware if you're planning to purchase that particular product!

2. I'm going to test in order to find the min. amnt. of peroxide that cures the problem. (Tell me if you want it to share here later...) OTOH, I'm not sure if there's any adverse effect in adding peroxide to the stock solution, both in terms of stability and picture-making. I would definitely like to have your comments and warnings (if any) on this issue. (Please note that I'm planning to use the same AFC for making Vandykes and/or Argyrotypes too!) Also, what else can I do to eliminate Iron(II) from the stock solution?

TIA,
Loris.