A few cleaners for cleaning copper utensils are usually available at
your local grocery or hardware store.  Look for the ones that claim
to remove tarnish instantly, such as "CopperBrite", "Twinkle" or
"Tarn-X".  These will be located along with the metal polishes.

A convenient way to clean copper, brass or phosphor bronze is to soak
the pieces in a solution of vinegar and salt.  The amount of salt added
to the vinegar doesn't matter much as long as it is dissolved.  Be sure
that your phosphor bronze is free from dirt and oil by scrubbing with
kitchen cleanser or detergent and water

A better cleaner that works great, too, is a solution of citric acid
and water, if you have convenient access to this chemical.  It's used
for canning foods.

These two solutions are slow acting and do not remove the base metal.
It may take an hour or so before the parts clean up.  Use a metal
polish or scouring powder to brighten up the metal parts after soaking
in these solutions.

Dennis Mead