Asteriated synthetic corundum gem stones and method and apparatus for their production

Claim 1

The process of claim 1 wherein the effective distribution coefficient of titania solute in the melt and the crystal grown therefrom is 0.1 whereby a rejection of said titania solute from the growing crystal occurs with a resultant increase in concentration of titania solute in a narrow diffusion layer of the melt adjacent the crystal interface, said excess titania concentration being transportable through said layer into the melt proper only by a time dependent diffusion mechanism and thereby dictating a maximum pulling rate for withdrawing the crystal from the melt without the incorporation into the growing crystal of portions of the melt containing excess concentrations of titania solute, comprising dipping a seed crystal into a localized region of the surface of said melt and initiating crystal growth thereon, and withdrawing said growing crystal from the melt at a pulling rate in excess of the maximum pulling rate dictated by the excess titania concentration at the growth interface, and preventing the incorporating into the growing crystal of excess solute containing portions of the melt by maintaining the localized region at a temperature supporting crystal growth while restricting the loss of heat by radiation from regions of the melt surrounding the localized region to maintain a higher temperature gradient through the diffusion layer into the melt proper than the temperature gradient which would normally occur if such loss of heat from the surrounding regions were not restricted, whereby portions of the liquid containing excess solute are not trapped and solidified in the growing crystal because of the higher temperature in the diffusion layer.