Figure 10. The effectiveness of trace elements in coloring corundum varies widely. These samples illustratethe effects of ~3,000 ppma Fe3+ (1.10 ct natural yellowsapphire in center), ~1,000 ppma Cr3+ (193.58 ct synthetic ruby rod at top), ~50 ppma Fe2+-Ti4+ pairs (2.54 ctblue synthetic sapphire wafer in center), ~20 ppmaMg2+ (40.04 ct purplish brown synthetic sapphire discin lower left), and ~25 ppma Cr3+ with ~25 ppma Mg2+(large orange boule on right). Photo by Maha Tannous