A short time ago I replaced some of my ageing Midwinter "Contrast" crockery with pieces of Thomas Medaillon White bone china, four 17cm sideplates. No metal trim, no decorations - just plain. I've now discovered that they are NOT microwaveable - even in a low power microwave and with food (2 frankfurters) sitting on them.
It would have been cheaper to get the higher cost Medaillon Platinum version - I wouldn't even have thought about putting them in the microwave! (Now after the event, I can't find any useful website relating to Thomas or Rosenthal products.)