When you microwave something, you input energy into its molecules. This can produce heat and stimulate a chemical reaction. This is great, if you are cooking food. Other materials don't produce a favorable result. Here's a list of things you shouldn't microwave and why. Actually, some are foods. Where possible, I included links to videos (screened for language and ads) so you can see what happens. If you're like me, you're curious, but don't want to destroy your own appliance or poison yourself with noxious vapors.
- CDs - Soooo pretty! The coating makes the sparks. If you nuke a cd, you'll get an awesome sparkler-like display, but you run the risk of a fire. Obviously, the cd will never work again. I would presume the vapors from the burning polymer are toxic.
- Grapes - I don't think you can make raisins this way. Your grapes will ignite, even though they are mostly water. It's a decent way to see the state of matter known as plasma, but you can ruin your appliance once the water from the grapes evaporates.
- Toothpicks or Matches - This is another example of plasma or ball lightning that can destroy your appliance. If you absolutely have to see charged plasma, get yourself a plasma lamp.
- Soap - Ok, maybe you should try this one. You get a cascade of bubbles. Very cool, decent chance of microwave survival, plus the soap is already inside for clean-up. Note that Ivory was used, which is actual soap. Other brands may not work as well. Another interesting note: the bubbly cloud that results has been tested and remains 'soap'. Apparently when you microwave soap, the water boils and forms soap bubbles. Heat causes air in the bubbles to expand. When the microwave stops, the soap re-solidifies.
- Hot Peppers - My dad once sent me some dried hot peppers from his garden. He recommended nuking them for a few seconds to make sure they were dehydrated before storing them. Um... don't! The capsaicin (chemical that is 'hot') is volatile. Your eyes will sting, your throat will burn. Oh... and the peppers may catch fire. I don't have a video, since there is nothing to see. Don't microwave any chemical you wouldn't want released into the air. Don't microwave dry materials.
- (Dry) Kitchen Sponges - If you nuke a wet sponge for 2 minutes, it will disinfect it (though it will stink up your kitchen). If you nuke a dry sponge, it will ignite. The WebMD article doesn't state this, but they should have: be sure you rinsed any cleaners out of your sponge if you intend to microwave it.
- Lightbulb - Don't do it. Even worse than this incandescent bulb would be a fluorescent bulb, because that would release toxic mercury vapors. Yeah, it might look cool, but microwaving these represents a real health hazard. Mercury vapor doesn't float out your window and vanish. Even worse, a microwave usually is located near food or surfaces used to prepare food. Lead is another toxic element that can be released from microwaving a lightbulb.