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why fading on edge of mirror?

Started by BABOafrica, 12/25/2012 10:37PM
Posted 12/25/2012 10:37PM Opening Post
I noticed last night when I was collimating my 10" dob that there are some blotches near the edge (about 1" wide along on the side of the mirror that sits lowest in the mirror box when viewing). More than blotches, they are areas where the surface is no longer giving full reflectivity and they look a bit yellowish.

Any ideas on what's happening?

I tried cleaning the mirror (not that it was especially dirty -- just some dust) but nothing changed.

I have no idea how old the mirror is, since I bought it second-hand, but the mirror does have the number 1959 written on the back.

It's a 1.5" thick, 10" pyrex mirror.


In lumine tuo videbimus lumen.

8O Home-made 10” Dob / Home-made 4” refractor

EPs: Konig 32mm (1.25") / Zhumell WF 30mm (2") / Nagler 13mm T1 / Orion Sirius Plossls 25 & 10mm / Zhumell Plossl 9 mm / Meade MA 9mm