Quoted from yancy:Zaccaria guru Dave Gersic says it's plastic with "vacuum plated vaporized aluminum." His amazingly thorough restoration of a bezel is documented here: http://www.zaccaria-pinball.com/projects/bezel/index.html
Vacuum metalizing is very common on plastic. I was not aware that this had ever been done on coin door parts by an OEM.
Interesting.
Terry.