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 1050°C. Every batch of porcelain is heat tested in our factory. Glaze – No softening occurs up to 1000°C, and it is extremely white. Resistance to Chemical Action – Resistance to acids and alkalies is excellent, except for hydrofluoric acid.