Something explosive?

Do you know of a chemical I can put on metal "stage" weapons that will make a crack, pop, spark, or bang upon impact? I'm afraid to google anything about it because I'll probably use a bunch of keywords that are wrong and then get arrested.

I'm doing costumes and props for some weird improv thing for a theater troupe, and it's crunch time.

The best way is the Highlander trick

In the Highlander movies and shows, the actors would each wear a wire going up their leg and this wire would attach to the base of their swords.  the wire would be attached to a power source and when the swords made contact, they'd cause sparks to arc between the blades.

http://tvtropes.org/pmwiki/pmwiki.php/Main.SwordSparks