I've used the Vinegar process and that works well. However, I've had good luck with Citric Acid. 2 tablespoons in hot water, stir, add brass, stir a little, and in less than 10 minutes you have clean brass. And the Citric Acid won't harm the brass no matter how long you leave it in the solution. Citric Acid can be found in any store selling canning or wine making supplies and is not expensive (and be sure to use glass or plastic containers and utensils, not metal).