1. During exposure, the ferric ammonium (III) citrate is reduced to the ferrous
salt:
Fe2(C2O4)3 -> uv -> 2Fe(C2O4)+2CO2
2. During development together with potassiumhexacyanoferrate(III) Turnbull's
blue is formed:
3Fe(C2O4)+K3[Fe(CN)6] -> Fe3[Fe(CN)6]2 + 3K2C2O4
3. Also during development, the potassiumhexacyanoferrate(III) is reduced to
potassiumhexacyanoferrate(II), thus forming prussian blue:
K4[Fe(CN)6]+2Fe(C2O4) -> Fe2[Fe(CN)6]+2K2C2O4
3Fe2[Fe(CN)6] ->o-> Fe4[Fe(CN)6]3
Klaus Pollmeier