This invention is a system and associated method for monitoring and controlling independently the supersaturation and halide ion concentration, during the precipitation of a silver halide emulsion in a precipitation vessel. The introduction of a silver salt is controlled in accordance with a predetermined program, which in turn is responding to the supersaturation signal measured in the vessel by a supersaturation sensor. The sensor is comprised of a true silver ion electrode and a silver-silver halide electrode. The introduction of the halide salt is controlled in accordance with the predetermined program, which in turn is responding to the halide ion concentration signal measured in the vessel by a silver-silver halide electrode and a reference electrode.