Microwaves are an electromagnetic field, which is why you shouldn’t cook in metal containers. Very thin metals such as the wire in a twist-tie, a gold rim or a bit of foil can’t absorb the current and are especially likely to heat up and spark. Some metals, like the rim of a frozen juice can, won’t spark. Some metals are okay in combination microwave/convection ovens. How can you tell if a dish is microwave-safe? Put the empty dish in the microwave along with a cup of water in a glass container. Microwave on high for one minute. If the dish gets hot, don’t use it. If it stay cool, it’s safe to use. Is all paper safe? No. Some paper is a fire hazard. You can use wax paper, cooking bags, parchment paper, paper plates and white paper towels. Don’t use recycled paper, newsprint or brown grocery bags. Recycled material may have minute amounts of metal that can cause a fire. White is usually safer than printed or tinted paper. Is it safe to use plastic wrap and other plastics in a microwave?