Is my mirror coating deteriorating?

[iceman]

Yesterday I took the mirror out of my 12" scope to wash it, and usually after rinsing with demineralised water, only a small amount of large droplets are left on the mirror, while the rest dries very quickly. The large droplets I then just dab dry.

Yesterday, I found that even while washing it, and then again when I set it to dry (after rinsing with demineralised water), the water was beading almost in rows and after rinsing, most of it still stayed on the mirror and didn't dry quickly like normal.

See attached pics.

Something wrong with my coating?

[stringscope]

G'day Mike,

My initial thought, based upon the 2 photos is that the mirror looks like it needs further cleaning. If you reckon the mirror really is clean then I don't know.

Have you tried shining a torch at the front of the mirror while looking through the rear? If the coating is deteriorating, you will be able to see the torch light through the coating. You will always get some pin holes, but if you can see most of the torch beam, then it is time to consider recoating.

Cheers,

[Garyh]

Hi Mike,
Like Ian mentions, put a torch on it or hold it up to a bright light source and look through the back. If you can see the light source and a large amount of pinholes you might need a recoat.
cheers Gary

[iceman]

hmm Ian you may be right - I have noticed it seems a bit 'stickier' when I washed it lately - it's possible there's some substance on the coating which is causing the water to bead like that and not wash/rinse properly.

Apart from normal detergent (which I've been using), what could I possibly use to remove any stickiness while still being gentle enough on the mirror coating?

Windex? If they use it on the large mirrors at Obsession then surely it'll be fine on mine?

[Screwdriverone]

Hi Mike,

I think I figured out what the problem is.....

STOP DRYING THE MIRROR ON THE STOVE!!!!!!

:rofl: sorry, couldnt help it.


Chris

[AlexN]

Try cleaning it with a 50-50 solution of 99% Isopropyl Alcohol and demineralized water.. The Isopro should take care of any residue/stick substance... I wouldn't advise using windex, it is likely to leave a fine filmy coating on your mirror which is likely to degrade the views/images.

Isopro should do the trick, failing that, it could be time for recoating.. How old is the mirror?? I wouldnt think the coatings would deteriorate in less than 4 or 5 years, that said, with peltier cooling, your mirror isnt exactly going to hold to the same standards as the usual 12" mirror...

Best of luck getting it sorted.

Alex.

[rmcpb]

All been said but by the way those drops are in rows it looks like some residue still on the mirror. How about another wash after a good soak?

[PeterO]

Still looks gummy. For what its worth I clean mine like this, comes up a treat every time.
http://www.youtube.com/watch?v=9Y8xFnXFVGQ

Peter

[ngcles]

HI Mike & All,

Alex wrote:

"Try cleaning it with a 50-50 solution of 99% Isopropyl Alcohol and demineralized water.. The Isopro should take care of any residue/stick substance... I wouldn't advise using windex, it is likely to leave a fine filmy coating on your mirror which is likely to degrade the views/images."

Agree with the isopropyl alcohol advice and it also cuts-down the beading effect as the water will tend to sheet-off rather than bead which in turn stops those annoying little dust-rings when the droplets evaporate. Personally, I don't think windex will leave much of a residue (if any) but I wouldn't risk it with the potential long-term effects on the coatings.

Don't be afraid to give it a good long (20mins) soak when you re-wash.

As others have advised, shining a bright light against the back of the glass in a darkened room will show pin-holes well and also reveal whether the coating is getting a bit "thin".

Good luck with it.

Best,

Les D

[Rodstar]

Mike, if you are referring to the Obsession DVD where Kreige demonstrates how to wash a large mirror in situ in the scope, he does not use Windex. He uses a spray bottle with distilled water and a bare drop of gentle detergent.

Good luck with sorting out your issue. It doesn't sound too bad to me in terms the likely very modest degradation in the visual observing you might experience, but I guess the imaging tolerances may be less.

[gregbradley]

RCOS recommended using Windex but with a gentle wipe with Kleenexes.

I found Bintel's UHTC cleaner works very well on any optic. And is streak free.

Perhaps you have some resin on the mirror like from pollen or trees etc.

Greg.

[astro_nutt]

Hi Mike,
I found a common problem with my mirror is the oil present in the air..from exhaust fumes, bar-b-ques, cooking etc will make their way and set on the primary mirror..so how do you clean a greasy plate?...place it in hot water and use detergent..but for my mirror I place it in warm water and gradually add more hot water to about 30 degrees C..then add the detergent mixture (one drop mixed into 500mls) and allow the heat to soften the oily film and the detergent to dispurse it for about 10 minutes...rinse in warm water and a final rinse in warm distilled water...
Cheers!

[netwolf]

Have you considered this stuff, Photonic Firstcontact its a spray on gell that you then peal off.
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/2280401/Main/2265915
http://www.photoniccleaning.com/

Video demo from NEAF
http://cloudynights.blip.tv/#900248
http://cloudynights.blip.tv/#900367

Looks pretty cool.

Regards
Fahim