This CoorsTek standard form porcelain evaporating dish is designed with a convenient pouring lip. Glazed inside and out except for rim. CoorsTek porcelain & ceramic labware has excellent thermal-shock resistance. It remains the responsibility of the user to determine the suitability for use. to prevent thermal stress cracks on porcelain ware, CoorsTek strongly recommends a heating/cooling rate not to exceed 200-degree celsius/hour. To prolong the life of your CoorsTek labware be sure to follow gradual heating and cooling rates. Use an oven or hot plate as an intermediate step when quicker heating/cooling rates are required. Gradually increase flame intensity when using a gas burner. Avoid contact of heated ware with a cold surface. Carefully inspect your ceramic labware prior to each use. Do not use any product that appears defective. Hardness of this labware is 57.5 on the Rockwell 45N scale. Refractory Qualities include a fusion point of 1670-degree celsius and a softening point of 1400-degree celsius.