This ruse consists of pretending to hand a spectator a copper coin and a silver one, while actually giving him two duplicate coins, say two coppers. Holding these in his closed hand, he returns either copper coin to the magician, convinced that he must be holding the silver coin, when in fact he has a copper one. This ruse was first described in Dr. Theodore Sack's “Silver-Copper” in Bruce Elliott's The Best In Magic, 1956, p.46.
See also: Copper-Silver Transpositions with a Copper-Silver Feke