It's a lean, green, killing machine—except when it hasn't oxidized, in which case it's a lean, red, killing machine.

Copper, the common element routinely used in the production of plumbing systems and electrical wiring, is a proven antimicrobial agent. Tarnished or not, copper, brass and bronze surfaces have been shown to kill most harmful bacteria—from antibiotic-resistant superbug staphylococcus aureus (MRSA) to the food-poisoning E. coli strains—within hours of contact. Scientists don't know exactly why uncoated copper and copper alloys have germ-fighting superpowers, but with the fear of a global pandemic following this summer's swine flu outbreak, they don't care as long as it works.

Copper's bacteria-blasting properties are as inherent to the metal as thermal and electrical conductivity and have been used, though not always understood, by humans since ancient times. Ancient Egyptians used copper vessels to sterilize drinking water, according to the New York-based Copper Development Association (CDA), while healers throughout the ages have recommended the red metal in treatments to cure everything from intestinal worms to...