Roland,

Would you object to this comment on silicone lubricant being
reprinted in my local club newsletter or website. It is an excellent
warning about careful choice of materials used to do a job.

Thanks,
bill

--- In ap-ug@yahoogroups.com, chris1011@a... wrote:
> In a message dated 5/2/2003 7:31:59 PM Central Daylight Time,
> ted@s... writes:
>
>
After some recent group discussions, I had placed an order for
several tubes of Dow high vacuum grease for distribution among group
participants since all the suppliers I could find had a minimum order
quantity. This grease is recommended for correction of mirror flop
issues on SCTs and greasing of focuser tubes.
> >
> >
>
Be careful with any product containing silicon oils (grease is a mix
of oil and solids). Silicon oils have a strong tendency to migrate.
They can migrate up to a foot over a year's time. If they get on any
optical surface, they will creep into the molecular structure of the
glass. If that happens, any metal or oxide coating on the glass will
lose its adhesion. The coatings will literally fall off, and there is
no way that any new coating will ever adhere again, even if the glass
is repolished.
>
> Roland Christen
>
>
> [Non-text portions of this message have been removed]