>>14182400It's pretty safe, but if you play with for too long you WILL crack some glass. My parents were pretty annoyed after I cracked 2 glasses and and one plate in the microwave while playing with plasma. I cracked quite a few glass jars as well. They last much longer if you keep the individual runs short, but that's boring.
That was something like 12 years ago, and that microwave still works just fine.
You don't need use grapes specifically either. Any flame can also absorb microwaves and get the plasma ball started. I liked to use matches and toothpicks. Even an unlit half burned one would heat up from the charcoal absorbing microwaves and catch fire on its own, and then the fun started.
