Aggressive mirror cleaning......!!

[NGC 1502]

Hi everyone.  PLEASE READ THE FOLLOWING WITH CAUTION !!  What’s described is a last resort if all else fails, and should only be attempted at your risk.  Aggressive cleaning of optical surfaces could destroy it and be an expensive mistake.

Lets start by saying that aggressive does not mean attacking with an abrasive substance or heavy rubbing  - DON’T DO THAT !!

Yesterday as I walked past my local branch of a well known second hand trader, I spotted a Skywatcher Heritage 130p complete with mount priced at £49.99.   I pondered for a moment, went in and asked to see it.  All looked fine except for two issues. The first was that the single stalk secondary holder was obviously bent causing the collimation to be wildly off. I thought that would be easy to fix and it was.   The main problem was that the primary mirror was very grubby indeed.  It looked like the scope had been stored mirror facing up without  being capped.  There was no signs of it being rubbed in a attempt to clean, I wouldn’t have bought it if that was the case.   The secondary mirror looked fine, presumably because that faces downwards.

On reaching home, the first job was to remove the primary cell complete with mirror.  Easy, four tube to cell screws, plus another that also secures the lower end of the dovetail.  Simple to remove mirror from cell.  In the time honoured way I left the mirror to soak in luke warm soapy water while I had a cuppa.

On returning to the job, I changed the water and using fresh top quality lint free wipes gently stroked the mirror surface underwater with frequent change of wipes. It made no difference.....mirror looked just as grubby.......repeated that process......no joy at all.

I decided that the very even looking coat of “grubbiness” could be some sort of airborne contamination from unprotected storage.  Maybe it wasn’t such a bargain after all.

I tried leaving the dry mirror face up on a level surface and filling the very shallow curve of the optical surface with 99% isopropyl alcohol.   Then a repeat of the previously mentioned soapy water clean.   The mirror looked a bit better but not much...

Repeated all of the above, with some improvement.  Then I recalled a post I’d read from Roland Christan of AstroPhysics fame, thats the low volume top quality manufacturer of triplet apochromatic refractors in the USA.   He mentioned that human saliva was great for cleaning optical surfaces, although in that case he’s talking about lenses, not mirrors.   So I tried gently licking the mirror surface, that definitely started to help.  Not altogether hygienic but I’ve survived to tell the tale !   Repeated the licking,  washed with soapy water then a thorough rinse.......BINGO  !!     A pristine mirror that looks great even under harsh lighting.

Reassembled, collimated, awaiting first light.  I now own more telescopes than clear nights in a year 😳

Cheers, Ed.

 

 

 

 

[Sunshine]

Amazing, you are a brave soul, i would have written that mirror off, licking it clean would have been so far from my train of thought. Maybe spitting on it and gently finger rubbing the spittle but, you say you actually licked it clean?? you my friend, should be issued the equivalent of the amateurs astronomers Nobel Prize or something. The story will be told at star parties.  One fellow will ask of another, as they glance at you from a distance, "who is that man?"... other man replies, "you don't know! that is the man who once licked his mirror spotless" a collective gasp is heard from everyone around and, they part as you walk the grounds. 

 

Edited February 23, 2020 by Sunshine

[NGC 1502]

Thank you Sunshine for your ‘tongue in cheek’ comments......but please remember that there’s sometimes  a very fine line between success and failure......

I’m contacting Walkers Crisps to suggest “mirror flavour” could be the next big seller 😁 and you heard that here first....

Ed.

[Macavity]

😛 lol. I always felt, as a solvent, isoproyl alcohol is a bit wimpish tho'!
I sense they don't like to sell absolute alcohol (ethanol) hic?!? Stuff like
Benezene is Carcogenic... Ether is Aneasthetic... BUT there is Acetone...

Dunno if you can readily buy it, but it's a good solvent... More polar?
Attracts different "muck" to Alcohol? Miscible with Water or Alcohol.
The main ceveat: it dissolves most Organics... PLASTICs notably! 😱

For cleaning optics, Acetone is mentioned (+water and isoproanol):
https://www.edmundoptics.com/knowledge-center/application-notes/optics/cleaning-optics/

Another thing to avoid is Acids OR Alkalis! Pretty sure your nice
Aluminium mirror would rapidly disappear leaving a glass blank? 🤣

Edited February 23, 2020 by Macavity

[mikeDnight]

A caustic soda bath will remove the aluminium from a primary mirror without harming the figure. Only wear marigolds and eye protection, do it in a well ventilated place not breathing in the fumes. After leaving the mirror in the caustic bath for a while, wash off using clean water, preferably distilled, and definitely do not lick! Even light rubbing of a primary mirror surface with a finger will add zones to the figure. Once clean then send it to be realuminized.

[Macavity]

I vaguely remember the words of "Sir Patrick" re. an un-silvered *reflecting*
SOLAR telescope. I have often found myself casually wondering! But then a
Herschel wedge still needs additional filters! (If anyone persues such ideas!)

The idea of "re-silvering" mirrors has often intrigued me. Even the modern
Aluminised ones doubtless lose reflectivity with time (Here the seaside). 😛

[mikeDnight]

1 hour ago, Macavity said:

I vaguely remember the words of "Sir Patrick" re. an un-silvered *reflecting*
SOLAR telescope. I have often found myself casually wondering! But then a
Herschel wedge still needs additional filters! (If anyone persues such ideas!)

The idea of "re-silvering" mirrors has often intrigued me. Even the modern
Aluminised ones doubtless lose reflectivity with time (Here the seaside). 😛

You still won't be able to look directly through an unsilvered / unaluminized reflector at the Sun. You can only use it for projection as the focused image will simply burn right through your cornea. I once tried just that, by using an A4 writing pad and bringing it to the point of focus, where it rapidly burst into flames. Great for cooking sausage though, if you're desperate for sausage!

Edited February 24, 2020 by mikeDnight

[NGC 1502]

3 hours ago, mikeDnight said:

You still won't be able to look directly through an unsilvered / unaluminized reflector at the Sun. You can only use it for projection as the focused image will simply burn right through your cornea. I once tried just that, by using an A4 writing pad and bringing it to the point of focus, where it rapidly burst into flames. Great for cooking sausage though, if you're desperate for sausage!

Years ago, some club members were doing public outreach using a 4” refractor to project the sun’s image onto a screen. One of the members held a pencil to the eyepiece to show the dangers involved, the wooden pencil quickly smouldered and gave off smoke.   As he withdrew the pencil, a bystander started to bend to look through the scope.......of course they were immediately prevented from doing that.......we were flabbergasted that having just seen what happened to the pencil anyone would want to put their eye to the eyepiece.

The above is regularly recalled when discussing solar observing because some will simply not grasp the very real dangers even with a totally obvious demonstration 🙄

Ed.

 

 

[Sunshine]

1 hour ago, NGC 1502 said:

Years ago, some club members were doing public outreach using a 4” refractor to project the sun’s image onto a screen. One of the members held a pencil to the eyepiece to show the dangers involved, the wooden pencil quickly smouldered and gave off smoke.   As he withdrew the pencil, a bystander started to bend to look through the scope.......of course they were immediately prevented from doing that.......we were flabbergasted that having just seen what happened to the pencil anyone would want to put their eye to the eyepiece.

The above is regularly recalled when discussing solar observing because some will simply not grasp the very real dangers even with a totally obvious demonstration 🙄

Ed.

 

 

Somehow, that doesn't surprise me at all.

[Timebandit]

On 23/02/2020 at 16:32, NGC 1502 said:

 So I tried gently licking the mirror surface, that definitely started to help.  Not altogether hygienic but I’ve survived to tell the tale !   Repeated the licking, 

 

 

 

 

 

 

I thought this was an April fools , but we are a bit off that date

 

Have you a dog or cat. Stick a pet treat over the mirror and they will do the licking/cleaning for you. I am not sure what the RSPCA may say about this though😀

 

 

 

 

[paul schofield]

This has give me an idea for Dragons Den. Excellent post, I'm still giggling. 😁

[Gasman]

II have some windows could do with a good clean, do you happen to travel Northwards? 😉

[NGC 1502]

On 26/02/2020 at 15:10, Gasman said:

II have some windows could do with a good clean, do you happen to travel Northwards? 😉

 

Just gimme the postcode and I’ll be there, now I’ve got the taste of grubby glass I think I’m hooked 😁