But metal isn’t prohibited all the time. Newer microwave models are designed to be used with small amounts of metal. Be sure to check your manual before trying this, however.

A large sheet of very thin metal, like a big piece of aluminum foil, can in fact heat up extremely rapidly, becoming so hot that it could start to burn the microwave. So don’t do that.

The company, which emerged from stealth on Monday with an $8 million Series A raise, is using “literally a microwave, but on steroids” to cast metal parts much quicker than metal 3D printing ...