It is a variation of applying chrome paint. During the process, it is darkened by varying the thickness of the reflective that goes over the base black. IIRC, If you stick to the basics, you get chrome, if you add more top coat, you get aluminum, add more and you get brushed stainless. Pretty complicated, and I am not a body man. I like it for its durability (automotive clear top coat). I like the weathered, polished look.
My body man is a hard-to-please custom car builder, and he liked the way it turned out. His only comment was that every single little pinhole has to be filled in order for the effect to be spot on. Almost all of that was taken care of in the primer/high build stages of prep. A few slipped by him. I said, "Hey! it's just a go cart!" He doesn't think like that about the finished jobs that leave his shop. Some info on chrome paint at his website--
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