The types of glazes used in hobby ceramics fall under the ‘low-fire' category since the kiln only uses the medium temperature ranges to mature the glazes
Oven and Microwave Safety
Glazed earthenware is not normally recommended as an oven-safe material, however, it may be used in the microwave safely. There have been instances of earthenware pieces cracking in microwaves when a small food item has been placed on a large platter. In these instances, a large differential of temperature between the area that is in contact with food and the rest of the platter can be great enough to cause a fracture.
Clay is basically a mixture of rock powder, that has been broken down by nature over millions of years, and water. There are various types of clay. These can be examined from two main perspectives: the geological origins of the clay ie: Primary and Secondary, and the type of clay body.
Although most glazes are fired in the 05-06 cone range always check the label for the recommended firing temperature.
Along with the color range, this is one of the more attractive reasons to use white earthenware. Firing to cone 06-cone 04 is well within the range of even the most geriatric kilns, and standard elements will last much longer than they will at stoneware Temps!