Glass ceramics (e.g. Ceran, Robax or Nextrema) are produced from glass melts by controlled crystallisation. These composite materials of glass and crystals have a high mechanical strength and can withstand temperatures of up to 950 °C. Their coefficient of thermal expansion is close to 0, so that even extreme temperature changes of up to 800 °C cannot harm them. Glass ceramics are therefore ideally suited as fire viewing or fire protection panels in fireplaces and furnaces, even for lining fire boxes, but also as parts in laser gyroscopes or as underlays in laboratories.
Nextrema from SCHOTT, for example, can withstand temperature shocks of up to 820 °C without any problems.