What makes a ceramic dish not dishwasher/microwave safe?

Question:I bought these really cheap ceramic mugs and plates. After using them for quite some time I noticed the writing on the bottom “not dishwasher/microwave safe”. The thing is I had already run them through the dishwasher and nuked them several times. Nothing seemed to happen, so what’s the deal? Are they now unsafe to use?

Answers:
What you need to look for is the "foot" on the bottom. If it is shiny then it is glazed and should not be a problem. My guess is that the foot is not glazed so it will feel rough and unfinished. In that case, you need to be careful not to let the dishes soak in water. The unfinished foot will absorb water and when you heat the plate (in the micro or dw dryer) the water molecules move around and can crack the glazed surface. As long as you don't leave them soaking or stacked with water between plates, you should be ok. (One other reason may be that some finishes have small amounts of metal which is not good for the micro.) If they are cheap enough, don't worry about it - just replace when needed. Hope this helps:)