This article is from the Model Rockets FAQ, by Wolfram von Kiparski with numerous contributions by others.
Copperhead igniters are actually two strips of copper wire with a
thin mylar insulating layer between them. To use these with regular
alligator clips you need to use masking tape to insulate opposite sides
of the igniter from each clip.
'Thin' (side) view of copperhead igniter: | | |______| < Motor with Copperhead inserted || Masking > || tape > || || ||< Masking ||< tape ||