You can give copper an aged look by using a liver of sulfur patina. It turns our metal a deep, dark brown. By then sanding the surface gently, you can then expose the copper and give your piece a satin finish. Check out the examples below.
This patina turns copper a beautiful blue color with variation in finish, opacity, and texture. This is achieved by creating a fume chamber of ammonia and allowing it to interact with sodium chloride - salt and water! This can also be done with vinegar instead of ammonia, but the finish is more green than blue.
After letting your piece sit in the fume chamber over night, take it out, let it dry, and seal it with lacquer for a lasting finish.