Vacuum deposition really brings back memories. Haven't heard or read those words in years. Back in the early 80's I developed a procedure to vacuum deposit pure aluminum on PMMA (ie, acrylic) discs then spin coat them with a clear lacquer that was cured with UV light. The finished product was commonly referred to as a VLP or video disc. Shortly after that, we developed a similar procedure to coat smaller discs (ie CDs). Yeah, some fond memories.
Now, back to our previous discussion. Sorry for the interruption.
It is literally spray on elemental silver with a clear coat. Long term out door use is not so good if it gets scratched it will tarnish just like a silver teapot. If you keep it dry and out of the sun its great.