Corning Completes Telescope Mirror Blank

Corning Incorporated has delivered the second of two mirror blanks for the GEMINI project telescope, a multinational collaboration including the US, UK, Canada, Chile, Argentina and Brazil. The mirror blank measures more than 26 ft in diameter and is about 8 in. thick. Fabrication of the Gemini II mirror blank began in 1992 by sealing hexagons of ultralow expansion glass into one monolithic, flat mirror blank. Fusion sealing was performed at temperatures exceeding 1700 °C. After fusion sealing, the 33-ton mirror blank was ground flat on both surfaces.