Uses "Top Job", or some mild diluted window cleaner. Only take off the Mud. Do not try to shine the buckle as you will decrease the value of the find. Only use a tooth brush and slowly take off the dirt. Hope this helps. If you take any other abrasive tool to scrub the buckle you might as well just go out blind folded, dig a hole, put the plate in and walk away so maybe in another 130+ years someone can find it the way that you have oringinally found it. Good Job!!