[ATM] Does exposed Pyrex lose polish over time?

[Douglas S Angle <Douglas.S.Angle@can.dupont.com>]

Bill T. wrote:
Now I know the answer is almost certainly a resounding “NO,” but I was
wondering if the bare Pyrex might have lost a bit of shine in this idle 18
months of direct exposure to the atmosphere.

Other's have answered that there should be no degradation on the surface,
and that matches what I learned in chemistry class.  I don't think it will
"lose it's shine", implying a macroscopic corrosion.  However, what I hear
from Al Ward (Moonward vaccuum coatings
http://www.angelfire.com/mac/moonwardvc/) is that the coatings stick better
to newly polished surfaces.  He recommends coating not more than about a
month after polishing.  As I understand it, airborne chemicals, and perhaps
oxygen itself don't react with the glass to cause corrosion, but stick to
the surface, altering it's surface characteristics.  The coating is then
attempting to stick to these adsorbed contaminants, rather than the glass
molecules.  Since the coaters wash the mirror with some pretty aggressive
chemicals (see: http://130.15.144.99
/rasc/pics/24inch/2002march23mirrorcoatingtriptoddo_20.jpg), I assume that
your giving it a rinse to remove obvious dirt won't fix this situation.

I haven't tested this myself, and don't have independant verification.  You
may want to talk to the coater first before deciding what to do next.

-Doug


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