The skull crucible process was developed at the Lebedev Physical Institute in Moscow to manufacture cubic zirconia.

[1] It was invented to solve the problem of cubic zirconia's melting-point being too high for even platinum crucibles.

In essence, by heating only the center of a volume of cubic zirconia, the material forms its own "crucible" from its cooler outer layers.

The term "skull" refers to these outer layers forming a shell enclosing the molten volume.

When the zirconium oxide is melted on the inside (but not completely, since the outside needs to remain solid) the amplitude of the RF induction coil is gradually reduced and crystals form as the material cools.