Patent ID: 8104309

Claim:
A method of making a quartz glass body, said method comprising the steps of: a) feeding a quartz glass-water mixture into a gypsum casting mold, said gypsum casting mold comprising an outer part and an inner part having respective shaping surfaces for contacting the quartz glass-water mixture and at least one of said inner part and said outer part having a corresponding duct system under at least one of said respective shaping surfaces, said duct system comprising a plurality of ducts in the form of textile tubes and at least one connector for connection of a compressed medium; b) drying the quartz glass-water mixture in the gypsum casting mold; c) during said drying of step b), putting an overpressure on the quartz glass-water mixture by applying the compressed medium to said corresponding duct system in said at least one of the inner part and the outer part; and d) transmitting or communicating said overpressure to the quartz glass-water mixture through said plurality of said ducts of said corresponding duct system in said at least one of the inner part and the outer part; e) during said drying of step b), applying a hydrostatic pressure on said quartz glass-water mixture in addition to said overpressure applied during said drying through said duct system; and f) after said drying of step b, removing a resulting green glass body from the gypsum casting mold, whereby during said removing a pressure difference is applied across the gypsum casting mold, or a portion thereof; wherein at least a portion of the shaping surfaces of the inner part are surfaces of a water-impermeable substance.