What metal is under the stainless layer when it wears of? I have this belt for several years now and the belt buckle is naturally subject to wear and tear.

On the most exposed spots the outer layer is now completely worn of and I wonder


Is this an example of passivation of the inner material?
What is the outer layer made of? Stainless steel?
What is the metal under the outer layer? It looks (and smells) like copper but why would they make it out of copper? Copper is – as far as I know – more expensive (by volume comparison, because the belt buckle can't be made smaller) than stainless steel? 
Wouldn't it be cheaper to make it only from stainless steel (assuming the outer layer is from stainless steel)? It would also be better from health perspective because I suspect the inner layer causes skin irritation.


I intentionally scrubbed the bottom edge of the buckle before taking the photo to reveal the real color of the metal, on the top edge it is presumably covered by its natural oxide layer (copper has it green, right? But it's just a thin layer so it can look different I suppose).

I am kind of ashamed answers to these questions aren't already known to me because this effect happens on a lot of daily used metal objects...
1 =no , 2= no, 3 Likely brass , 4= no. The buckle is likely a brass although the bottom edge where you polished it is copper color . That could result if you used some cleaning agent. It could be made from copper but modern mass production would use brass. It was plated with nickle and / or chromium. Nickel plating is usually put down first , under chromium plating.