Al or Ag (Alum or Silver) mirrors: Which is best?

[Star Hunter]

I've got some finished mirrors here and unsure which is best, Al. or Silver coats with an over-coating. Has anyone used a silver coated mirror scope and how does it stack up to Al in reflectivity and longevity?

Much appreciated.

JB

[bojan]

My Coulter Optics 10" mirror is Al + SiO2 coated and dates from 1980..
Washed 3 or 4 times so far, and survived the impact of secondary couple of year ago..still works OK.
There was a discussion on the topic here on forum earlier:
http://www.iceinspace.com.au/forum/showthread.php?t=86474