"The furnace in the third method of smelting ores has a tap-hole likewise open, but the furnace is higher and wider than the others, and it's
bellows are larger; for these reasons a larger charge of the ore can be thrown into it. When the mines yield a great abundance of ore for the smelter, they smelt in the same furnace continuously for
three days and three nights, providing there be no defect in either the hearth or in the forehearth. In this kind of a furnace almost every kind of accretion will be
found. … However, because large charges of ore are smelted uninterruptly, and the melted material runs out and the slags are skimmed off, there is need of a second forehearth crucible,
into which the molten material runs through an opened tap-hole when the first is full. When a smelter has spent twelve hours labour on this work, another always takes his place. The ores of
copper and lead and the poorest ores of gold and silver are smelted by this method."