Porcelain Buchner funnels include fixed perforated plates. Funnels are glazed on inner and outer surfaces except for the rims.Thermal Shock Resistance - average coefficient of expansion from 20 C to 200 C is 3.56 x 10-5, gradually increasing to 4.69 x 10-5 at 1050C. Every batch of porcelain is heat tested in our factory.