Chances are that gold finish you're looking at on your booster is cadmium plated. It's one of very few " plating " processes that can be performed on steel, which I assume your booster is made of. Anodizing and iriditing is for Aluminum alloys, or possibly substrates that have been " coated " with aluminum. There is some work in the area of dying oxides on steel , which is more or less a controlled rust. Oh well , enough of that.