So for Road to Glory the majority of the props needed to look worn and aged.  Through trial and error I found that for metals you need to first apply a base coat, I used spray paint, to the metal so the actual coat of paint won’t chip off.  Next, you use sponges and a variety a watered down version of the colors you need to give the metal the proper texture and look.  Finally you apply a clear layer to add protection to your paint and that is how you age metal through paint.