I have used Aldrich's FAC (brown 16.5% - 18.5% iron) cat. No. 22,896-2
for making Cyanotypes. It seems to give a slightly less dense blue than
the green version, is less light sensitive.
As a matter of interest:-
The BJP Almanac for 1959 gives the following formulae for Ferro-
Prussiate sensitisers using either the green or brown versions:-
Soln. A
FAC (green) 250 grm
FAC (brown) 187 grm
water to 1000ml
Soln. B
Pot. Ferricyanide 92 grm 137 grm
water to 1000ml
Dissolving freshly precipitated ferric hydroxide in a soln of ammonium
citrate in the correct proportions, then evaporating is supposed to
produce the brown version. Perhaps the green version could be produced
by using an excess of ammonium citrate.
Alex
Alex Nanson
Gloucester UK