A crucible furnace comprises an enclosure having an outer casing 20 internally lined with thermally insulating material 21 surrounding but spaced from a crucible 22 so as to define a circular flow path 23 around the crucible. A gas fuelled reversing burner system is provided having two burners 24 and 25 each with an associated heat regenerator 42. The burners 24,25 are operable alternately as firing burners and as flues. When one burner, say burner 24, is firing, the hot combustion product gases from that burner flow in one direction along the flow path 23 and around the crucible 22 and leave the flow path through the burner 25 in flueing mode, whilst in the alternate cycle the hot combustion product gases from the firing burner 25 flow in the opposite direction along the flow path 23 and leave the flow path through the burner 24 in flueing mode.