Cleopatra and Nefertiti plates from UAR

I have had these for some time and there is more to them than I initially thought. they are between 48-61 years old. (Made in the UAR) and all that was initially visible was the copper parts. The rest of the plate area was black. That changed after I applied some Maas cleaner to a lighter area of the plate. The end result was a lot more detail and the color of the removed soiling was solid black (no green). While the plates are relatively heavy for their size, none of the metal is magnetic. Any idea of what the non copper metals are? Are the exposed bust details silver?

 

Welcome CryHavoc.
It is not likely to be silver, but other metals can tarnish as well. The non-copper metals would also be base metals. Others will probably know the exact alloys, and will no doubt be along later.

Your time frame is correct, btw. For those who don't know the UAR or United Arab Republic, it was originally a union between Egypt and Syria which only existed between 1958 and 1961, but Egypt kept using the name until 1971.