Cleaning Optics - Methyl Alcohol 99% (CH3OH)

[capncurt86]

I have had my used 8" Dob for several months and had a hard time seeing DSOs.  I have attributed it to light pollution and my lack of experience.  A few weeks ago I bought a used, but newer Nexstar 5se.  I have been finding out that the 5" SCT performs much better than the 8" with the same eyepieces on the same night with planets.  The 5" SCT is a 1250mm FL, F/10 and the 8" dob is a 1200mm F/6, so both in the medium speed range.  Last night I finally found the Hercules Cluster which was awesome! But it was only fractionally better in the 8" than the 5".  The 8" should gather 250% more light than the 5" plus it has a smaller obstruction so it may be better than that.  The view of M13 and M5 last night WERE better in the 8" but not 2.5 times betters, maybe 10-20% better.

That led me to ponder the reason.  Both scope are well collimated, at least as best I can get without a laser collimator.  The only difference is the 8" has a dirty primary mirror. Everywhere I have read here and other forums and sites say not to clean it, BUT it looks bad.  The previous owners had the telescope for 5+ years and I don't think they kept it in a clean place with the cover on.  I also noticed that the primary mirror had been turned slightly and the place where the clamps were is much cleaner than the rest of the mirror.  (Kind of where you move a sofa and the carpet under the feet is new compared to the rest around it.)  I also had a XT6 that was new that I just sold to compare it to.  The XT6's mirror was flawless when a flashlight was shined on it compared to my 8".  So this evidence is leading me to believe that the dirt/"stuff" on the primary is obstructing my view.

 

Now to my question.  I work in a lab where we have high quality 12" parabolic mirrors used for schlerin imaging.  These are $10k mirrors that we cover when not used.  We try to clean them rarely because it could damage them if we are not careful.  Our cleaning process is to first use canned air to get the dust off.  Then spray 99% methyl alcohol on them followed by dragging (not wiping) a Kimwipe through the methyl alcohol.  This does a decent job and does not harm the mirrors. 

Can I use the same method on my Dob mirror?  Are there any special coatings that may be removed if I used methyl alcohol?  Has anyone done this before?

 

Thanks!

Curtis

[Bizibilder]

Unless you are sure about the coating I would stick to water as a cleaner.  If you use warm water (body temperature!) and a pure cotton wool swab you should get the mirror clean easily enough.  Maybe a tiny amount of soap would help.  Rinse with warm water and then with fresh distilled water.  Leave propped on edge to drain and dry.  Should work without any damage.

[capncurt86]

3 minutes ago, Bizibilder said:

Unless you are sure about the coating I would stick to water as a cleaner.  If you use warm water (body temperature!) and a pure cotton wool swab you should get the mirror clean easily enough.  Maybe a tiny amount of soap would help.  Rinse with warm water and then with fresh distilled water.  Leave propped on edge to drain and dry.  Should work without any damage.

Thanks.  That's seems to align with other cleaning how to's. I just don't like the idea of using tap water with all those impurities.  I guess I could heat up some distilled water.

[101nut]

I wouldn't be too concerned about the tap water for most of the washing. The vast majority just sheets off, so do a final rinse with distilled and allow to dry.

AndyG

[capncurt86]

Thanks gents.  For anyone's future reference, I have since contacted Orion to see if Methyl Alcohol will damage the mirror's coatings.  Their answer was "maybe".  They did however, recommend isopropyl alcohol.  So I will be buying some 99.9% isopropyl alcohol and Kimwipes.

 

Thanks again.

[PHIL53]

I would stick to simple tap water (have done more than once, actually more times than necessary !) as shown here:

https://www.youtube.com/watch?v=9Y8xFnXFVGQ&list=PL8pYZmh4J6lNZZHE1DvZjI9FXKaJVzfXb&index=8

 

[Astrobits]

If you Google " Aluminium and Methyl alcohol" then you will find that these do indeed interact. The Methyl alcohol acts rather like an acid, particularly if it is anhydrous, albeit rather slowly at room temperature. Other alcohols are not innocent either.

If I have to use a solvent other than water+soap then Acetone or Methyl Ethyl Ketone is my choice.

Nigel

[hughgilhespie]

Acetone or MEK would be fine. But, just to clarify, water is a 'stronger' acid than methanol and would be more likely to attack aluminium. In fact, if you remove the protective oxide film from aluminium, water does attack the exposed metal. Fortunately for astronomers, aluminium is always covered with a continuous, self-repairing oxide film. It is also normal to overcoat the aluminium coating on mirrors with a thin, transparent, layer of sand and, as people who live near the seaside can testify, sand does not dissolve in water.

Regards, Hugh

[Astrobits]

I agree that water will attack Aluminium provided the oxide layer is disrupted which water alone cannot do. When Methyl alcohol ( Methanol ) attacks aluminium, it reacts with the oxide layer and the product ( Aluminium Methoxide ) is soluble in Methanol. This allows dissolved oxygen to react with the fresh Al surface and corrosion occurs in a continuous cycle. Methanol in fuel has proved to be a problem because of this reaction with aluminium components.

Nigel

[capncurt86]

I successfully cleaned my mirror tonight. Woot!  All these posts about leaving it alone scared me, but it took less than 30 min and went flawlessly.  I also found out that the previous owner didn't tighter the mirror to the mirror holder enough to where it was sliding around.

 I decided to go the water and a little soap route.

I first rinsed  the mirror under running tap water.  Then I put it in a large plastic dish with a tiny bit of dish soap and enough water to just cover it.  I bought Kimwipes and dipped these in the soapy water and drug them over the mirror without any pressure at all.  Then I picked the mirror up and swished the water over it and repeated with the Kimwipes and swish about 10-15 times. Then I rinsed under the running water again.  Finally I filled the dish with distilled water and did a few final rinses.  Then I used  canned air to get most of the water drops off.

In the end, it was definitely worth it!  That mirror was 5+ years old with so much crud on it, I'm surprised it worked.  Now I just need the moon to go away so I can test it on some DSOs.

 

 

Thanks all for the help!

[Ouroboros]

I worked with high power lasers and optics most of my working life.  Cleaning mirrors, including aluminium ones, was a necessary and fairly routine activity. We always used high purity organic solvents. Often this meant working with whatever came to hand in the lab. Methanol, ethanol, isopropanol work well.  Acetone can be good for removing greasy marks, but often left a white residue that had to be removed with another solvent. The technique we used was  to blow away dust particles with a pressurised air canister. It is absolutely essential that no dust particles are left on the mirror that might scratch it when the mirror is wiled.  We then used large lens tissues, some as big as a man-sized paper tissue.  The tissues might be used in different ways. Tissue could be laid across the mirror, a little solvent dropped on, which then sticks the tissue to the mirror by surface tension, and then slowly dragging the tissue sideways off the mirror. Alternatively, the tissue might be folded into a pad, onto which a little solvent was dropped, and wiped gently but firmly across the mirror's surface. Tissues are only ever used once, and then discarded to avoid reintroducing muck onto the mirror, or worse an abrasive dust particle.  The tissues,  made by a company called Whatman if you're interested, are much better in my experience than the lens cleaning tissues I've bought occasionally from astronomical equipment suppliers. One advantage of using organic solvents is that they evaporate quickly. So you could whip out the optic, give it a quick clean, pop it back in and get working again very quickly. 

What we never never used was water. In fact it was one of the things that really surprised me when I retired and took up astronomy that people used water to clean telescope mirrors. Water?  In the sink? With detergent? What? I should coco!  But it works. In many ways I think it's better.  You never have to touch the mirror's surface. You've got an inexhaustible supply of cheap solvent (tap water) in which to bathe, agitate or flow across the surface of the mirror. Residue from tap water is quickly flushed away by a little de-ionised or distilled water.  Water is safe - unlike organic solvents which are both toxic and flammable.  Plus water doesn't appear to do aluminium mirrors any harm, not in the few times you're ever going to clean a telescope mirror in its lifetime anyway.  It just takes a little longer because mirrors have to dry. But that's OK. It's a hobby! 

[Dave In Vermont]

I would agree that using distilled water is the best option - or listen to Doc Clay - a famous expert on SCT's and other optics. He has an excellent guide, which I'll link a pdf. for below:

ASO fine optics CLEANING SYSTEM - Part I & II.pdf

One common mixture is to mix a little iso-Propyl Alcohol (C3H7OH) in a liter of distilled water with just a drop of liquid dish-washing detergent. Then do your original drag of a clean surgical-wipe across the mirror in one direction - one surgical-wipe per swipe. Then rinse with distilled water.

I would council against using Methyl Alcohol. It absorbs through intact skin, and poses a high inhalation hazaed - as it is VERY poisonous - attacking the optic-nerves and can cause temporary blindness which may become permenant at higher doses. It's not worth the hazards unless working in a fume-hood.

Only clean your mirror (or any optics) if they are really grimey. Dust, streaks, or anything seen with a torch/flashlight won't adversely harm your views. Cleaning without a need may do so easily.

Dave - a chemist