Getting back to cleaning the heavy dirt, I would brush this lightly with a soft bristled brush such as a toothbrush. If heavy deposits remain you may let it soak in hot water with a touch of blue dawn dish detergent. And go back over it again with a few brushings. You don't want to use a wire brush or harsh chemicals on the brass. Once you get it cleaned to your satisfaction, don't use any cleaner to polish the brass. You want to leave as much patina on the brass as possible, but I'm sure you already knew this. Give us some before and after pic's when you get a chance. Happy Thanksgiving to you and your family.