Newtonian Mirror Cleaning

[Wez]

Heya All,



First noob question from me (many more to come).
The Telescope I've purchase (SkyWatcher 400) had been in the shop for a year before I purchased it.


So the mirror seems foggy when I look at it during the day and slightly dirty.
Is the light foggyness expected in a Primary mirror? And is there a recommended way to clean the mirrors.


I'm a perfectionist so happy to work out the ideal technique to do clean the mirror.
I did email Skywatcher but got no reply from them.

[sunslayr]

I think the general consensus is dipping it in warm water with a mild dish washing detergent and then air dry.

[glend]

There are many internet threads on mirror cleaning, do a search on Utube to start.

[Startrek]

I clean the primary mirrors on my 6” , 8” and 12” newts as follows -

Prepare laundry sink area bench with clean towel , 2 litre bottle of distilled water , half a dozen cotton balls and a few cotton tips

1/ Carefully remove mirror from scope and lay upright on clean towel

2/ Use hair dryer on cold to blow off any residual dust

3/ Hold mirror under spout in sink under warm water , not to strong , just light stream for a minute

4/ Repeat item 3 but this time place a few drops of plain washing up liquid on mirror and using a damp cotton ball , lightly work in a circular motion from centre to outside of mirror

5/ Rinse off in cold water and check mirror is clean , if not repeat item 4 and 5 again

6/ Pour a litre of distilled water over mirror whilst holding mirror on a 45 degree angle , let drops roll off and much as possible
7/ Lay backside of mirror on clean towel and remove any residual droplets with a cotton tip ( light dab only not wipe )

8/ Leave mirror to completely dry indoors and then re install back into scope

The above works on my mirrors which are 3 to 4 years old anc are in good condition

Hope the above is of some help
Cheers
Martin

[croweater]

Hi Wes, follow Martins' excellent instructions and you'll be fine. I would just stress with step 4 no pressure. Very light with the cotton ball. Use a new one if you repeat step.
Also once the mirror is back in the scope don't panic at dust specs you accumulate. A bit of dust becomes normal. It will likely be a couple of years before it needs to be done again really.
Cheers Richard. :)

[notoriousnick]

As above, but don't forget to check the secondary mirror as well. If relatively clean, then OK, but sometimes these can also collect a lot of gunk.

[bojan]

Use cotton or microfiber cloth and rinse with demineralized water before drying.

[glend]

As we see, there are many variations on the same theme. I am a big supporter of the old folded paper towel technique, in which the pointy end of a paper towel very effectively wicks water drops off mirror surfaces without actually touching the mirror.

[sunslayr]

Woops, good point it's important to rinse after. I've found the yellow glass cleaning microfiber towels you get at Bunnings in those bags of microfiber towels are quite good, they seem to have a much tighter weave and don't leave anything behind.

[Wez]

Thank you all,



I shall do as instructed here, perhaps without any contact first to see if the misty colouring goes away. If it doesn't change then it really isn't that dirty and I'll leave it be.


I had read ISO alcohol was good but not mention of that here. I have some 99.9% stuff for resin print cleaning but is that useful or jsut go with detergent and water?

[bojan]

Just slowly running water from tap, then a drop of dishwashing detergent + fingers & soft cloth, then rinse in distilled or demineralized water, then remove droplets with tissue then dry.

[DavidU]

I use the method above but use my hand instead of cotton etc, skin will not scratch anything,
There are a few videos on this subject.

[Wez]

I did a write up on how my meaning all went from everyone's input and thought I would post it up here. I took some photos as well I'll post after..


So here is my breakdown of the clean. The mirror is now WAY better i'm very happy. I made a list of all the recommendations but ended up evolving my own process.
I did take photos I'll put up but didn't catch every stage.

Cleaning Round 1
- Ran water over the mirror, rocked mirror in water to get waves across surface - visibly removed floating bits
- Ran single finger over surface very gently with few drops of detergent in the water - could see the mist being wiped off even under flowing water
- rinsed with de-ionised (de minteralised was sold out where I went)
- Dried with paper towel dabbing at remainined water droplets (actually touching mirror)
Results were good. 80% of the surface issues were gone. Once I looked over it with a bright light I could still see remaining dots (on the surface I presumed). They looked to be in clouds patterns (I think this is aluminium particles probably from same factory)
Mirror handled the contact I did without any presence of marking.

Cleaning Round 2
- pool of water in mirror, lots of hand soap. Using all fingers ran over the surface more thoroughly with more pressure
- Same rinsing as above
Thought this was perfect until looking at it with multiple bright lights. Still tiny specs remained. I would say this was 95% clean now

Cleaning Round 3 - Hardcore more
- Tried 99.8% IPA on cotton bud direct to tiny specs. With scrubbing some of the specs went but not all. The cotton bud left blue steaks from the IPA I would guess.
- Gave up on cotton bud as the results looked poor and didn't seem very effective
- IPA on microfibre cloth folded to a new edge every minute or so seemed to pick of a decent number of the specks and clear away the blue mist. This evolved to hard scrubbing with the cloth and still no negative effect on the surface
- Finally found the remaining specs that still wouldn't budge with the hard scrubbing would come off if I used my finger directly on the dot and scrubbed.
- I had to shake out the cloth as fibers were coming on the mirror but continually scrubbing and shaking the cloth between wipes and slowly I was able to remove all the fibers (well most).
Eventually removed all but a single dot that I gave up on.
Now 99.99% clean. As a failed perfectionist (joke intended) that's passable


So finally thoughts...
- The mirror can hack waaay more that I expected. That final dot I even used my fingernail on in the end and still no surface damage (and it still defeated me)
- The specks may not be on everyones mirrors but I think they were from being in the same factory that did the aluminium coated and floated through the air and settled on the mirror. So not all mirrors may have it.
- De-ionised water was good but I never actually rinsed my final clean as the buffing was basically dry with IPA evapourating.
- I'm not sure the IPA was essential but it worked
- Fingers are amazing cleaning implements!

[Wez]

Here are some photos from the original mirror removal, after the second round of cleaning and then after the final round of cleaning

[notoriousnick]

Looks like you got the mirror to where you want it :thumbsup:.


Though most just stick with detergent and water, I gave up on that as I could not get rid of all the marks - including blue haze and other, likely non water soluble marks.


Now acetone is my best friend :D. I suspect that once you have carefully removed anything gritty, friction between fingers (or cotton wool) and the mirror surface is unlikely to damage it. My eleven year old 10" Dob mirror remains unscratched.

[Wez]

Yes the mirror was far hardier than I was expecting which is great for me :)