Hard drive platter as flat mirror

Some time ago, I disassembled some old hard drives with the kids (including one that was donated to the cause by my employer's IT services), and extracted magnets (fun, as long as you're careful) and platters.  The platters gave me the impression of high quality first-surface mirrors, and I've been looking for a use for them.  I've put one into my so far not very successful solar projector project as a heliostat.

I was just playing with looking at stars reflected in this platter through my 15x70 binoculars, with only one eye.  There was some unidirectional glare from Venus, but stars looked pinpoint.  I was only hand-holding the binoculars, so the test isn't great.  And it would have been better if the central hole was blacked out.  This isn't a very demanding test, higher magnification would be much better, but it's a promising start.