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Dishwasher and Microwave Safety for Ceramics
"Do's and Don'ts"

Microwaves and Ceramics

First of all, no metals should be used in microwaves. This will cause 'arcing', i.e. a spark jumps from the microwave to the metal, possibly damaging the unit. This means that ceramics with metal lustres or onglazes such as gold, silver and copper, should not be microwaved.

Secondly, microwaves heat food by agitating water molecules, which then get hot. If a ceramic dish or cup is low fired, it may soak up some moisture into the clay body. If this moisture gets heated enough, it will turn to steam and expand, possibly causing an explosion. Not only would the ceramic item be lost, but the microwave might sustain considerable damage. Because of this, I would recommend to only microwave porcelain and stoneware, or earthenware that is vitrified enough not to soak up moisture. If in doubt, hold the piece on the palm of your hand. Carefully knock it with a knuckle (make sure you don't knock it to the ground!). If there is a clean ring, the piece should be dry, whatever it is and probably safe to microwave. If it sounds dull, it probably has some moisture in the body -- it would be better not to risk it. (If it sounds really dull, with a short 'buzzing' sound to it, there probably is a crack somewhere.)

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