The change to the lance-based furnace increased oxygen utilization to 95% and the cycle time was reduced to a little less than eight hours, “but the grade of the doré which could be economically produced was poor.” The doré from the new furnace still contained about 0.8% lead and 0.4% copper. It was also found impractical to cast anode plates of doré directly from the Sirosmelt furnace, so the Sirosmelt doré had to undergo a further refining step in a reverberatory furnace, together with a sodium nitrate flux.
