Within a vacuum chamber or skull furnace having opening thereinto a closeable passage for a removable ingot mold there is a furnace structure not occupying the entire vacuum chamber for producing a pool of molten metal from which the ingot is to be poured, the furnace apparatus including at least one electrode with a fluid-cooled arcing surface and a magnetic field coil for substantially continuously moving the arc around the arcing surface. The skull furnace includes means for feeding material to the molten pool.