Accu-Glass’ Sapphire viewports are rated for both high and ultrahigh vacuum applications. The use of high purity sapphire and low expansion alloys allow these viewports to be repeatedly baked out at temperatures up to 350°C. Sapphire is a synthetic, hexagonal single crystal anisotropic material which displays substantially different physical, thermal, dielectric, and optical qualities when measured along different axes. The crystal orientation of our sapphire viewports is normal to the optical axis, also referred to as a 90° orientation. All viewports up to one-inch in diameter are made with UV grade sapphire. Viewports larger than one-inch in diameter are supplied with regular grade material.