Citric Acid works really well for cleaning tarnished brass. Found some of my Father In Laws old tarnished brass and amazing how it looks after the citric acid and a little tumbling. This link is where I got the info.
http://castboolits.gunloads.com/showthread.php?83572-Citric-acid-brass-cleaner
http://castboolits.gunloads.com/showthread.php?83572-Citric-acid-brass-cleaner
