Metal Containers and Metal Decoration
Never use metal or metal-rimmed utensils in the microwave oven.
Microwaves cannot penetrate metal. They will bounce off any metal object in the oven and cause arcing, an alarming phenomenon that resembles lightning.
Metal shields the food from microwave energy and produces uneven cooking. Also avoid metal skewers, thermometers, foil trays, metal-rimmed or metal-banded dinnerware, casserole dishes, etc. The metal rim interferes with normal cooking and may damage the oven.