SEARCH Articles Figures Tables A schematic diagram of the skull melting apparatus. Not shown are protective screens around the vacuum cylinders, a transparent fused silica sleeve between the skull crucible and the r.f work coil, and a fume hood above the apparatus. to mechanical pump. [Publishers Imprint] See Also: A schematic diagram of the skull melting apparatus. Not shown are protective screens around the vacuum cylinders, a transparent fused silica sleeve between the skull crucible and the r.f work coil, and a fume hood above the apparatus. to mechanical pump.