The Plates of Wrath

Dear Tricia, I put a ceramic plate in the oven for 10 minutes at 150 degrees and it broke in half. What's the dealio?

Damn, that sucks. I bet you had a real mess to clean up in your oven after that. If you're like me, you probably just took out the plate and set the oven at "self-clean" for a few hours while you went out for cocktails. And if not... well, damn. That sucks.
Ceramic dishes that aren't oven safe have irregular pockets of air inside of them that expand when they get hot. Then they explode all over your oven and ruin your reheated dinner. Ceramic dishes that are oven safe are treated on the outside to keep the air pockets from doing this. To check to see if yours is in the latter category, just flip it over and check the bottom. That's where the manufacturer tells you if your dishes are dishwasher, microwave, and/or oven safe. If it says nothing, then you're S.O.L. and probably got your dishes at the Dollar Store. (Hey, I don't judge. I have gone on many $30 shopping sprees there.) However, because manufacturers are afraid of being sued by crazy people looking to get rich, there are lots of microwave-safe dishes that are indeed oven safe but won't say so on the bottom. If you're willing to chance it, you just have to do a couple of things.
First of all, don't take a cold plate and put it in the oven. The drastic temperature change will definitely cause it to break. Make sure that the plate is room temp, OK? (I learned this first hand when a fellow culinary student and I were using a blowtorch on a dessert in cold champagne glasses. Because I'm from Texas and she was from the Virgin Islands, "cold" wasn't in our vocabularies, so we broke about half a dozen glasses before we figured out what was happening. Our teacher wasn't a big fan of us.) Take a cookie sheet, put it in your 150 degree oven, and put a dish towel on it. Then put your plate on the towel. If you're wanting to warm up plates before you put food on them, stack them in the oven on the towel/cookie sheet combo.
Unless they specifically say they're oven safe, do NOT put china in the oven. You're just asking for a shard in the eye then, and sure, it's all fun and games... until someone gets expensive china in the eyeball.
If you've got dishes that don't say "oven safe" and you don't want your oven looking like something that happens at a Greek Wedding, just use a casserole dish or a cake pan to reheat your food: something that is meant for putting in the oven. Happy reheating!