Sapphire crystals up to 34 cm diameter, 65 kg, are grown in production using the heat exchanger method (HEM). The properties of sapphire that are important for high technology applications make it difficult to grow as large high-quality single crystal boules. The HEM has been adapted and efforts to grow 50 cm diameter sapphire crystals are in progress. Current applications require the upper limits of sapphire properties to meet current systems demands of the combination of size, purity, crystal perfection with optimum optical and mechanical properties.