Optical glass is manufactured in the United States by one company only, but that company manufactures a wide range of glass types and could produce any additional types for which a demand might develop. Blanks for prisms and refractor lenses of moderate size are available from the same source; larger sizes probably could be obtained, but only on special order. Disks for reflecting telescopes are not made of optical glass, and methods for manufacturing them have been developed by one of our leading glass companies. As a result, the manufacture of reflector disks of the largest size has been put on a production basis. The characteristics of optical glass are made clear by a short discussion.
GEORGE W. MOREY, "The Availability of Optical Glass in America," J. Opt. Soc. Am. 28, 5-5 (1938)