Since earthenware is porous, ceramics are easily damaged if exposed to extremely hot temperatures, such as boiling water. Majolica is low-fired earthenware and has a tendency to "craze" (form miniscule lines) with repeated use. This crazing is a part of the unique nature of majolica and does not have any significant effect on the piece itself. To reduce crazing, we recommend that you place a metal spoon in your mug or any ceramic vessel before pouring hot liquid to absorb some of the heat. Dishwashers vary and if yours has a low-energy/cool dry cycle, it is possible to use one and not encounter any adverse effects. We do not recommend repeated microwave usages.