In order to break a car window's tempered glass, the porcelain insulator inside of a spark plug can be used. Unglazed porcelain is rated 7 on the Mohs scale of mineral harness, while glass is rated 5.5.Continue Reading
To shatter a car window with a spark plug:
Spark plugs generally use a porcelain insulator. Break the spark plug with a hammer to obtain the porcelain insulator inside of the spark plug.
Throw a piece of porcelain at the car's window to break it. The small pieces of porcelain can easily break a window when they are thrown at it.