<< Now the problem is should I add a small quantity of citric acid to each
batch to make it like the old "impure" stuff? >>
Well, I think the answer to that is no, though you could supply it with a
suitable note.
I wonder if the exact composition of ferric ammonium citrate may depend on the
method of making it. The brown and the green forms have different formulae in
the books of course.
Peter Marshall
On Fixing Shadows, Dragonfire and elsewhere:
http://faraday.clas.virginia.edu/~ds8s/
Family Pictures & Gay Pride: http://www.dragonfire.net/~gallery/
and: http://www.speltlib.demon.co.uk/