Re: [ATM] silvering vs mercury

["Bob May" <bobmay@nethere.com>]

The aluminum coating on a mirror should be just thick enough to
block the light from passing through the coating.  It also needs
to be evenly enough applied so that there aren't splotches of
coating in some areas and thin in others.
Many of the coatings done are just barely transparent enough so
that you can dimly see the sun through the coating.
I'll note that experiments have been done to parabolize a
spherical mirror in the chamber by the proper application of the
aluminum and they worked although the surface finish really
wasn't that great.  The Twyman book has a bit on the work done.
Bob May
bobmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net
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