corundum, synthetic corundum.7, Czochralski, gems

This past summer, a manufacturer of synthetic corundum shared the Czochralski-pulled synthetic ruby shown in figure 20 with staff mem-bers of the East Coast lab. The modi-fied triangular mixed cut weighed 115.56 ct and was completely trans-parent, with a strong red color that had no purple or brown components. Although natural ruby may be found in large sizes, it usually contains so many inclusions that the diaphaneity is translucent rather than transparent, One area of the pavilion of this large synthetic showed fine curved striae, but otherwise it was free of inclusions or variations in color. Because of the large size and trans-parency, a slight doubling of the pavilion facet junctions-a rare sight in corundum, which has low birefrin-gence-was visible through the table. The manufacturer of this synthetic ruby reports that he is using a new process in which growth is controlled on a scale of several inches, with the goal of producing material that is entirely free of inclusions or disrup-tions of the crystal structure (such as twinning or graining) up to sizes as large as 500+ ct.