Metal gravy boats should never be heated in the microwave or oven. The gravy can be heated on the stove in a pan or in the microwave and poured into the gravy boat. Metal will spark and does not heat well in the microwave and in the oven gets too hot to hold the handle. You can pour warm water in a gravy boat or very hot water and dump it out before pouring in the gravy and serving. Some gravy boats come with lids and electric warming trays. Stoneware and porcelain gravy boats should not be heated in the microwave or oven because it gets too hot to handle. Better to heat the gravy and pour it in.