Custom fabricated sapphire viewports and sight windows for builders of UHV systems and process machinery that permit viewing in hostile environments are available from Meller Optics, Inc. of Providence, Rhode Island. Meller Sapphire Viewport Windows provide Mohs 9 hardness which is second only to diamond and are suitable for applications from UHV to 10,000 psi and from cryogenic to 1,000°C, depending upon configuration. Manufactured to precise customer specifications, these sight windows resist chemicals including fluorine to 300°C, most acids, and are impervious to fast moving water and particulates such as blowing dirt, and sand. Available in a variety of configurations and sizes from 0.25” to 10” dia., and 0.5mm to 1” thick, Meller Sapphire Viewport Windows can be fabricated with stepped edges and elliptical edge shaping, holes, slots, and wedges for mounting, and include A/R coatings. They exhibit flatness to 0.5 fringes HeNe and parallelism from 20 to 2 arc/secs. Meller Sapphire Viewport Windows are priced according to configuration and customer requirements. Price quotations are available upon request.