No actually I don't own an airbrush yet. The weathering is done with strategic spray painting and small model brushes with watered down acrylic paint.
Distance from the nozzle of the spray paint can to the subject plays a huge factor when you don't have an airbrush. The farther away the lighter the coat and spread of the paint coverage. So the hammered steel farther away from the subject being painted over the black plastidip gives a weathered appearance. Make Sense?