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Re: [ATM] Aluminizing
Hi,
Mark Holm wrote:
> It doesn't say so on their web site, but I think Clausing goes that big.
> http://www.clausing.com/
I think they can go as large as anyone, but they are PRICEY,
particularly once you go over 12" in diameter. This is for Beral,
which has NO overcoating. About $300 to coat a 16" mirror with Beral.
Ouch!
> They have been in business since 1927 and have a good reputation among
> amateurs. The last time their name came up on this list, there were
> several favorable comments and no (that I can remember) negative ones.
> They have specifically advertised for amateur business since at least
> the 1950's. More than one atm (including me) has commented that their
> "Beral" trademark coatings seem to hold up quite well.
This is what I have seen myself, and heard from others. Draw your own
conclusions
> With reasonable
> care, and a not too awful environment, ten years seems a minimum
> lifetime. I have seen closer to 40 years on at least one mirror. Of
> course, if you live in a dusty alkaline desert, you may not get that.
Older Clausing coatings seem to last a very long time, and were a good
value. I have seen this on many occasions with others' mirrors and my
own. 10 years plus is not uncommon.
Newer coatings seem to be less robust based on personal experience and
what others have told me.
I have some recent Clausing coatings myself. Not bad, but there's
lots of metal on the bevel, and there were some pinholes in the
coating, too. I was not thrilled.
I saw a 16" (recently) beral-coated mirror from our observatory fail
in 5 years. This coating is shown at
http://bi-staff.beckman.uiuc.edu/~melockwo/telescopes/16in_CUAS_cass/mirror_removal.html
Scroll down towards the bottom.
In Clausing's defense, this mirror likely got quite a bit of
condensation on it over time, making it a very harsh environment.
However, we'll be getting an overcoated aluminum coating this time -
at HALF the cost. Personally, I'm done with Beral, at least the
current version of it.
Mike Lockwood
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