re-aluminizing mirrors

I've heard conflicting information about how long modern overcoated
mirrors last before they need re-aluminizing. I know there's no one
definitve answer, but I'd like a ballpark idea. About 10 years? 25
years?

Patrick wrote:

I've heard conflicting information about how long modern overcoated
mirrors last before they need re-aluminizing. I know there's no one
definitve answer, but I'd like a ballpark idea. About 10 years? 25
years?


I have a Meade DS-10 which I bought in October of 1982. I had it
recoated this past
February. After 20 years it was showing some minor sleeking and
moderate "spider web"
scratches.

I also have an Edmund Scientific 3-inch reflector which I bought in
1959. After 44 years it
has no sleeking and moderate "spider web" scratches.

The advantages of clean Ozark Mountain air. 8-)

Dale

On Sun, 21 Sep 2003 19:09:17 -0500, Dale ...reflected:

Patrick wrote:

I've heard conflicting information about how long modern overcoated
mirrors last before they need re-aluminizing. I know there's no one
definitve answer, but I'd like a ballpark idea. About 10 years? 25
years?


I have a Meade DS-10 which I bought in October of 1982. I had it
recoated this past
February. After 20 years it was showing some minor sleeking and
moderate "spider web"
scratches.

I also have an Edmund Scientific 3-inch reflector which I bought in
1959. After 44 years it
has no sleeking and moderate "spider web" scratches.

The advantages of clean Ozark Mountain air. 8-)

Dale

That sounds more like the effects of the thermal expansion
coefficient, that is, the expansions and contractions of the figured
glass blank over time, which should be less noticeable in a three-inch,
if I'm understanding the process correctly.

I can't imagine Meade having figured those primaries with blanks
made of other than ordinary plate glass. Else, the blank was subjected
to extremes of temperature year after year, as in its having been stored
in an unheated/uncooled garage or room, not to mention the effects of
moisture.

In any case, you've some dark skies, no doubt, to put that 10"
to good use!

Alan