Ceramics are quite inert by nature, and there is good reason why many of the oldest human artifacts are ceramics. In essence the material is akin to stone, although much more brittle. The best storage is upright (or upside down) on a padded mat or cloth, in a cupboard, shelf, or cabinet. Ceramics can typically withstand a wide range of temperatures without taking any damage, so long as they have time to adjust to the new temperature.