Product information from ceramic artist Samantha Norha:

It is thrown from porcelain, altered, and decals are applied before glazing to cone 6. Microwave and dishwasher safe. 

About: 
- Approx. 1" h x 4'' w.
- The clay and glazes are lead-free and food safe.
- While very durable, microwavable, and dishwasher safe, I highly recommend not microwaving ceramic ware, as it has been proven to be stressful on the wares. To prolong the life of your handmade pottery hand washing is not necessary, but recommended. Do not pour boiling, stovetop water directly into handmade ware, as this can sometimes cause stress on some items. “Pre-warming” your cup by swirling warm/hot tap water prior to pouring your fave hot beverage is recommended.