[Chippy (Nick)]

Hi All,

I've got an 8" GSO dob and a while back got a drip of water on the mirror. At the time I didn't realize how easy it was to take the primary cell out, so although concerned, I just left it - hoping it would eventually evaporate away with no problem.

After a while I noticed that there was still a mark where the water droplet had been (2 in fact - as the drop had "splashed"). I still thought it was probably just some dirt or residue left behind - but the mirror had gotten a bit dirty (some dust and bug grime) so decided to clean it...

Well turned out that the mark where the water had been - had cleaned the silver right off the glass. Once I got the mirror out I could see there were actually lots of other tiny "splashes" as well where the silver was "gone"...

Its not a large percentage of the mirror surface (~1%) but still I was disappointed. I guess there must have been some acidity in the water that reacted with the coating? I was under the impression that there was a protective coating over the mirror (silver) finish - so didn't think that would happen so easily!!!

I cleaned the mirror as per instructions here - using just a drop of detergent in luke warm water etc - very carefully & gently - with just a very light dab using some cotton stuff from the chemist. It actually didn't clean all of the grime off - but much better, and I didn't want to risk any further damage to the surface.

After the mirror dried I noticed that around the edges of the mirror - the silver seemed to be slightly "dimmer". Not particularly noticeable, but detectable if you looked closely. So it seems that even my very careful cleaning process may have "dulled" the mirror finish slightly on the edges. Its not a huge issue and the scope still seems to function quite well - but it does concern me that if I need to clean the mirror again - will it become 'more dull'??

Curious to know if anyone else has come across similar, or any comments, etc. I take it there's no point trying to get the glass re-mirrored as it just wouldn't be worth the cost. Just wonder whether my mirror had less coating on it or something?

Regards,
Nick.