The material of the mould has to be suitable to withstand the process temperatures without undergoing deforming processes. Therefore, the mould material choice depends critically on the transition temperature of the glass material. For low-Tg-glasses, steel moulds with a nickel alloy coating can be used. Since they cannot withstand the high temperatures required for regular optical glasses, heat-resistant materials such as carbide alloys have to be used instead in this case. In addition, mould materials include aluminium alloys, glasslike or vitreous carbon, silicon carbide, silicon nitride and a mixture of silicon carbide and carbon.
