Large size Sapphire crystals up to 4'' boule are available from Dayoptics, As the hardest of oxide crystals, sapphire has a combination of optical and physical properties that make it the best choice for a variety of demanding applications. Sapphire maintains its strength even at high temperatures. It has good thermal properties, excellent electrical and dielectric properties and is resistant to chemical attack. These properties encourage the use of sapphire in aggressive environments where reliability, optical transmission and strength are requied.