The terms “dishwasher” and “microwave safe” mean, as they concern pottery, that the dishes won’t be damaged when used with those appliances. Most properly made dishes are dishwasher and microwave safe, but there are some exceptions and considerations.
Exception: Metallic overglazes are details that are applied through a second, lower-temperature, glaze firing. They’re most commonly silver and gold in color. When a piece has these details applied it is no longer microwave safe, and will spark like aluminum foil when microwaved. Overglaze details also tend to be softer than regular glazes, and while they can still be dishwasher and food-safe, they’ll last longer if hand washed with a soft sponge (avoid the scrubby kind).
Consideration: Clay bodies, maturity, and porosity are factors that interact with how the dishwasher and microwave safety of a dish can change, depending on how it’s treated. A clay body is the type of clay that ceramics are made of, and most fall into three broad categories: porcelains, stonewares, and earthenwares. Within each category of clay body are numerous recipes with varying colors and maturation temperatures. The maturation of a clay body is reached when it is fired to its optimum temperature to achieve a dense and durable product. Even so, a mature earthenware will tend to be more porous (have a higher porosity) than a mature porcelain (which is practically a glass when fired to full maturity). The higher a pots’ porosity, the more water it can absorb, which becomes a danger to the dish regarding microwave safety (and freezing). This is all to say: an earthenware dish can be dishwasher and microwave safe, but if it has absorbed too much water by being put through a dishwashing cycle, or soaking in a sink full of dishes, it can be detrimental to use it in a microwave before it’s had time to dry out because of the potential for rapid conversion of the water into steam which can damage the dish. Also, a clay body with very high iron content (usually dark-colored earthenwares) can become very hot when microwaved.
to be continued…