(Source : Basic Photography - Michael Langford)
Sol A
Water 700 ml
Copper sulphate crystals 25 g
Potassium citrate 110 g
Water to 1 litre
Sol B
Water 700 ml
Potassium Ferricyanide crystals 20 g
Potassium citrate 110 g
Water to 1 litre
Working solution : 1 part A + 1 part B.
Results range from warm black to purplish-red, depending on length of immersion.
Wash as normal after toning.