Patent ID: 6928838

Claim:
A method for forming silica glass elements, comprising the steps of: providing a top die assembly comprising a top mold die made of isotropic carbon and a core mold peripheral of which is held by said top mold die and made of vitrified carbon and a bottom die assembly comprising a bottom mold die made of isotropic carbon and a core mold peripheral of which is held by said bottom mold die and made of vitrified carbon; interposing a silica glass material between the top and bottom core molds of the top and bottom die assemblies; pinching the silica glass material disposed between the top and bottom core molds in a close contact condition so that heat transfer from the top and bottom core molds to the silica glass material becomes possible; heating the top and bottom die assemblies and silica glass material in this pinched condition to a prescribed temperature; and press forming the silica glass material which has been heated to the prescribed condition.