Tall form crucibles include covers. Crucibles are glazed on inner and outer surfaces except for the outside bottom and rim. Autoclavable. Withstand temperatures to 1150 degrees C. To prevent thermal stress cracks, we strongly recommend a heating/cooling rate not exceeding 200 degrees C per hour. United porcelain crucibles offer excellent resistance to acids and alkalies except for hydrofluoric acid. Resistant to thermal shock with an average coefficient of expansion from 20 degrees C to 200 degrees C is 3.56 x 10-5, gradually increasing to 4.69 x 10-5 at 1050 degrees C. Every batch of porcelain is heat tested in our factory. Every batch of porcelain is heat tested in our factory. No glaze-softening occurs up to 1000 degrees C and it is extremely white. Resistant to acids and alkalies, except for hydrofluoric acid. Capacity 30ml. 6 per pack.