PRODUCTION OF SPURIOUS PARTIALLY HEALED FRACTURES IN SYNTHETIC CORUNDUM THROUGH HIGH-TEMPERATURE FUSION

For more than a decade gemologists have been making heat-treatment "residue" calls on so-called flux-healed natural rubies and sapphires. These judgements as "flux-healed" with "residue" are based on the visual appearance of certain partially-healed fractures and parting-planes that have an intricate web-like glassy look to them. Through experimentation, virtually identical partially-healed cracks in synthetic and natural corundum have been produced by heating in air with no fluxing agent, at temperatures ranging from 1800°C upward, toward the melting point of corundum. This high-temperature heating has also resulted in the formation of lamellar twin planes which become readily apparent when viewed in crossed polars. These high-temperature heat-fused cracks experimentally generated in Czochralski-pulled and flame-fusion synthetic rubies and sapphires look virtually identical to certain inclusions we commonly associate with natural rubies and sapphires that have been subjected to what is called a flux-healing process. If no contradictory visual evidence is observed, then synthetics containing such inclusions could be mistaken for heat-treated natural gems.