Washing a primary mirror.

[Quark (Trevor)]

Hi All,
I have held the opinion for a considerable time that washing a primary mirror was akin to an act of heresy. An act of someone with too much time on their hands.

Recently I discovered Mike's very well illustrated article on this subject in the "Projects & Articles section of IIS.

A friend ounce asked me how to do this and my advice to him was to go and mow his lawn and clean his car, maybe then this urge might pass. He was determined though, so went ahead and in his attempts to clean his mirror he managed to rub through the mirror coating in several places.

However, after reading Mike's article I must admit that I am beginning to waver and so I am seeking feedback from any forum members that did, in a moment of weakness, wash their mirrors. How successful was it and did they end up with any water marks?

Also wondered at the difference between distilled and demineralized water.

Regards
Trevor

[GeoffW1 (Geoff)]

Hi,

After doing a lot of research here on the forum and elsewhere I came to these conclusions from it all:

- washing if carefully carried out does no damage. The method is found here on IIS

- there is no point to washing the mirror frequently as it takes more than just a bit of visible contamination before performance is noticably degraded

- some types of contamination such as seaside salt air deposits and cockatoo poop do need to be removed quickly

I have washed my main mirrors twice and could detect no damage caused by this.

Distilled water is evaporated to steam and then condensed again and therefore should have no minerals or dissolved materials in it, but unless also filtered it could have a little dust in it.

Demineralised water is passed through a series of resins which remove dissolved materials, and then a membrane which filters out solids, even down to bacteria depending on the standard used.

I don't believe there is any effective difference for mirror rinsing, but I'd be interested in other comments.

Cheers

[leon]

I have done it a number of times when I had my 8 inch reflector, which has now gone to another good home.

Anyway, it is not a daunting as it is made out to be if one is careful and follows a few basic rules.

It is really this easy, just fill a clean sink or basin/bowl with luke warm water, and a few drops of dish washing liquid, and swish it around a bit until it is mixed in with the water.

Take you mirror by the edges only and completely submerge in the container/sink, and just swish it around as well with the water flowing over all the mirror, a few minutes is plenty, or as long as you like really.

Take it out rinse under the tap to remove all soapy water, and finally rinse with distilled water, then just stand it on end and let it naturally dry.

It really is that easy, and it wont be damaged, just dont put your fingers all over it.

If you like you can also swab it under the washing water with some cotton wool, if you do everything under the water before the final rinse, it will be all good.

Leon

However just an EDIT,, I have done it this way, but you do it at your own risk, it is a careful/common sense approach.

[Starkler (Geoff)]

I think that the vast amount of light scattering crud can be removed without touching the mirror surface at all. This includes loose dirt and water soluble contaminants which dry onto the mirror after condensation evaporates.

A rinse under a running tap, followed by a soak in warm water with detergent, and then another tap water rinse followed by a final rinse with distilled water will fix all but the cruddiest of mirrors as far as visible difference at the eyepiece goes.

[NQLD_Newby]

I have cleaned the primary mirror on my 4.5" reflector a couple of times using the exact method described in the article you have mentioned and have found absolutely no damage was done, and perhaps because of the small size, (less light gathering ability), I actually did noticed a huge increase in performance. I haven't had my 12" long enough to gather enough marks to do it yet, but I have no reservations what so ever, and can say that when the time comes I will be doing it also.

On your other point regarding the distilled/demineralized water difference. My lovely wife runs all drinking water through one of those filter jugs. I used it to clean and rinse my mirror (not tap water as mentioned above), and as stated earlier have seen no evidence of damage. I can't rememebr what the article says about tap water, but I was concerned regarding the minerals and chemicals added at the water treatment plant, so chose to use the demineralized water for all stages, just to be safe. Hope this helps.

[Glenhuon (Bill)]

I'd go with the advice on the distilled water. A few years back in WA when I was Chlorinator service man we had 10 days worth of chlorine gas dumped into the drinking water in a WA town in 2 days due to a dosing fault. It was stronger than pool water and made bicarb of soda fizz when added.
Dread to think what it could do to a mirror coating.

Bill

[GeoffW1 (Geoff)]

Originally Posted by Glenhuon

I'd go with the advice on the distilled water. A few years back in WA when I was Chlorinator service man we had 10 days worth of chlorine gas dumped into the drinking water in a WA town in 2 days due to a dosing fault. It was stronger than pool water and made bicarb of soda fizz when added.
Dread to think what it could do to a mirror coating.

Bill

Hoo hoo, I bet that made the undies fall to bits after being washed

Cheers

[rmcpb (Rob)]

Washing a mirror is just part of the maintenance program of a reflector. If done carefully then no damage will occur. I have washed both my mirrors many times and they are still in really good nick.

Take your time and don't put any pressure on anything that comes in contact with the surface like cotton balls, etc and you should be OK.

[astro_nutt]

Hi all
I have found that sometimes not all the dirt comes off when you wash it..so it's best to leave it alone..also...some may experience a swirl pattern after washing/rinsing as it happened to me..I found the cause to be a greasy substance being smeared by water pressure from the tap..(which I no longer do!!)..now I soak the mirror and gradually warm the water to about 35 degrees C before adding a drop of baby shampoo (diluted) to help lift the dirt off...after about 15 minutes of soaking...rinse gently with tap water followed by distilled water..leave standing on it's edge and remove any drops with a corner of a clean facial tissue..(just touch the drops, not the mirror!)
Even with a slight film on the mirror (which is only visible when you shine a torch on it) it doesn't affect the image quality!!!
Cheers!!

[5ash (Philip)]

Hi ill put in my 2 bobs worth with respect to a 13" mirror i washed for someone .The mirror was in a telescope that had been left capped in an observatory , but on inspection was covered with condensation and some dirt. All i did was to rinse under slow running water and swab ( no pressure) with weak detergent in quadrants similar to the method used to clean a SCT corrector plate . Then finished by rinsing with distilled water followed by absorbing remaining water drops with optical lens tissue. If i had a rocket blower i might have been able to remove most of the droplets without the tissue. The mirror showed no signs of scratching with this technique.
regards philip