A non-wetting melt forms droplets at the grain corners and is unable to flow. A similar phenomenon is the way that water beads up on a car after it has been freshly waxed. The properties of materials change as a function of the amount of pressure that they are under, and pressure increases rapidly with increasing depth in the Earth. The wetting properties of metallic melts may change with pressure, and we can only learn this by doing experiments at the pressures equal to those deep within the Earth. One device, called a multi-anvil press, generates pressure using several stages, the last stage being eight tungsten carbide cubes that press on the experimental assembly.
Heat is generated by passing electric current through a furnace within the assembly.
When we examined the experiments that had been squeezed and heated, we found that the sulfide melt is non-wetting. That is, it forms beads at the grain corners and does not connect into channels along the grain edges. Below is a photo of one experiment run at 10,000 atmospheres pressure and 1500 degrees Celsius. These microstructures indicate that the Earth's core could not have separated by metallic melt dripping along the grain edges of solid silicate. This implies that the core separated when planetary bodies were much hotter, perhaps almost completely molten.