I am going to be the outlier again here, but I have used vinegar, salt and water to clean some of the blackest brass you have ever seen. It just plain flat works. De-cap the brass with a universal decapping die, and put the brass into a bowl with a cup of water, a tablespoon of salt and about two quarts of water. I use hot water because it dissolves the salt and increases the cleaning action. Wait about 15 minutes, take the brass out and immediately rinse it, and I mean rinse it well. Then take the brass out and spread it on a towel to dry. Leaving it overnight works very well.
I typically use a tumbler to finish the work, but I have found that sometimes that is unnecessary.
Finally, fwiw, I have also used a packet of lemon flavored Kook-aid and two quarts of water to clean brass, so long as the tarnish isn't extensive.