Porcelain. Microwave and dishwasher safe. Do not overheat in a microwave or heat without water. Do not use abrasive cleansers or steel wool. Product size and shape varies in each item due to manufacturing process. Appearance of color glaze unevenness varies in each item. Some products may take on scorched-like texture on the surface. It is an unique glaze effect called "yo-hen", unintended color transformation show on the ceramic and porcelain after firing.