This paper discusses various issues surrounding the metallurgical control for furnaces, especially focusing on processes with long time-constants and metallurgical memories'. Examples will focus on furnaces accepting particulate and sometimes ill-defined feeds, eg submerged-arc furnaces, blast furnaces, secondary scrap smelting operations, recycling operations, waste incinerators, etc. Generally, because of the usually higher metallurgical time constant of these furnaces, these reactors have to be controlled in a feed-forward manner by the use of a hybrid of black box' or empirical and grey box' semi-empirical first principles metallurgical modelling and simulation techniques in a supervisory metallurgical control capacity.