Crack Balls

It’s fireworks time! Skylighter.com has a recipe for a more powerful version of those balls that bang when you knock them together. You paint smooth rocks with a mixture that contains powdered glass, potassium chlorate, and sulfur (all disclaimers in place). Then let dry. Drop or throw the rocks, and they’ll “bounce” repeatedly with a loud explosion each time.
Link (scroll down to middle of page).