Verdigris - a.k.a. that crusty green stuff. While it adds character, it also leaves unsightly pits in the metal. Verdigris could be either copper acetate, copper sulfate, or copper chloride. It commonly is caused by the tannins in treated leather reacting with copper (or the copper in brass & bronze alloys).
Fill an ALUMINUM bowl with 1/2 cup baking soda dissolved in 4 cups HOT water.
Dip the corroded pieces in the bath and let them sit for a few minutes. Due to toxicity, keep your hands out of the bath, use a string or wooden skewers to manipulate the pieces.
Repeat until the corrosion is gone. You may have to replenish the bath if the verdigris is extensive.
Rinse the brass thoroughly with hot water and dry it with a clean cotton rag.
Apply oil or other presrvative