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  #21  
Old 04-11-2009, 06:40 PM
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Yes but the Al coating is applied in a vacuum so oxidation will not be a major problem particularly if the protective coating was also applied before the mirror was exposed to air. My concern is simply based on the integrity of the protective coating considering their micron thickness. Mirrors that are exposed to the environment such as the case in open tube and truss frame designs have to have their mirrors recoated periodically as the Al coating some how comes in contact with oxygen (eg the coatings fail) and dulls due to oxidation and the formation of AlO3. Could it not then be possible that 2-propanol used as a cleaner might also reach the surface Al ? I imagine any scope mirror that did not have protection against oxidation would have very little usefulness beyond 48Hrs as the mirrors would dull rapidly. Just as an aside, I did a little experiment today. Freshly cut Al does indeed react with with 2-propanol but very very slowly. It took about ten minutes for the surface to visibly dull.

Mark

Last edited by marki; 04-11-2009 at 06:51 PM.
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  #22  
Old 04-11-2009, 07:34 PM
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All this talk of chemistry and labs stimulated my safety gene. Be careful with isopropanol:

- extremely flammable
- nasty in your eyes
- don't want to breathing it in too much while you're agonising over your optics

Probably why the chemist was worried about selling. Really just requires the care and respect you'd give while using any solvent.

Safety rant over now....
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  #23  
Old 04-11-2009, 08:36 PM
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Quote:
Originally Posted by marki View Post
Yes but the Al coating is applied in a vacuum so oxidation will not be a major problem particularly if the protective coating was also applied before the mirror was exposed to air. My concern is simply based on the integrity of the protective coating considering their micron thickness. Mirrors that are exposed to the environment such as the case in open tube and truss frame designs have to have their mirrors recoated periodically as the Al coating some how comes in contact with oxygen (eg the coatings fail) and dulls due to oxidation and the formation of AlO3. Could it not then be possible that 2-propanol used as a cleaner might also reach the surface Al ? I imagine any scope mirror that did not have protection against oxidation would have very little usefulness beyond 48Hrs as the mirrors would dull rapidly. Just as an aside, I did a little experiment today. Freshly cut Al does indeed react with with 2-propanol but very very slowly. It took about ten minutes for the surface to visibly dull.

Mark
I doubt that it was the IPA dulling your Aluminium. Freshly cut Sodium reacts slowly with IPA, that's what we use to get rid of excess Sodium without too much of an exotherm. Probably dissolved Oxygen in the solvent. AlOxide coatings on fresh aluminium are essentially impervious to liquids, though gas molecules are small enough to permeate slowly. Alkaline or acidic solutions will slowly dissolve the AlOxide and dull the Aluminium surface, which is why you shouldn't leave your mirrors wet. Also remember that most aluminium available to us is an alloy, not pure aluminium as would be vacuum deposited.

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Originally Posted by RobF View Post
All this talk of chemistry and labs stimulated my safety gene. Be careful with isopropanol:

- extremely flammable
- nasty in your eyes
- don't want to breathing it in too much while you're agonising over your optics

Probably why the chemist was worried about selling. Really just requires the care and respect you'd give while using any solvent.

Safety rant over now....
Geez, I'd hate to take you to a petrol station...

Petrol
- extremely flammable, forms explosive mixtures with air readily
- nasty in your eyes, on your skin (especially in those sensitive areas)
- don't want to breath in too much
- until recently actually contained a heavy metal poison (Lead)
- until recently contained a confirmed carcinogen (benzene)
- contains CNS toxins (Xylene and Toluene)

Amounts in use, IPA about 125 ml, Petrol usually over 40 litres...

Cheers
Stuart
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  #24  
Old 04-11-2009, 09:31 PM
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How about Windex?. I tried it once, and it gave a very clean, streak free finish, better than anything else I have tried. Worried me a bit though, there is no mention of chemicals used, but the instructions say dont use on acrylic,fiberglass,painted surfaces, waxed, polished or varnished wood, or tinted windows. What do you think would be in it?, would it damage Al coatings?.
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  #25  
Old 04-11-2009, 09:41 PM
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How about Windex?. I tried it once, and it gave a very clean, streak free finish, better than anything else I have tried. Worried me a bit though, there is no mention of chemicals used, but the instructions say dont use on acrylic,fiberglass,painted surfaces, waxed, polished or varnished wood, or tinted windows. What do you think would be in it?, would it damage Al coatings?.
From memory the windex formulation had ammonia in it, avoid it for that reason alone.

Cheers
Stuart
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  #26  
Old 04-11-2009, 09:58 PM
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Bunnings paint section: diggers isopropyl alcohol @ 100%. Its an easy and cheap alcohol to distil so I don't doubt it. Comes in a spray bottle to boot. I usually dilute it to 70:30 using de-ionised water and it works a treat. I also have and tried the very high analytical grades of isopropyl alcohol (2-propanol) at work and the diggers version does exactly the same job. Will not affect UHTC coatings on meade optics. Low grades will have impurties such as 1-propanol and water left from production.

Mark
Tks Mark, good ol Bunnings.
I have been using the Bintel fluid and its OK, but I still used pure Iso that I had from an Orion optic cleaning kit and this does the job superb but I ran out last time I cleaned my corrector. BTW the Meade site recommends at least 90% or better Iso so diggers at 100% makes me feel better. I will pick up some next time I am at Bunnings.
Here's the link if anyones interested.
http://www.meade.com/manuals/lx200/apxe.html

Matt.
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  #27  
Old 04-11-2009, 09:58 PM
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Quote:
Originally Posted by rat156 View Post
I doubt that it was the IPA dulling your Aluminium. Freshly cut Sodium reacts slowly with IPA, that's what we use to get rid of excess Sodium without too much of an exotherm. Probably dissolved Oxygen in the solvent. AlOxide coatings on fresh aluminium are essentially impervious to liquids, though gas molecules are small enough to permeate slowly. Alkaline or acidic solutions will slowly dissolve the AlOxide and dull the Aluminium surface, which is why you shouldn't leave your mirrors wet. Also remember that most aluminium available to us is an alloy, not pure aluminium as would be vacuum deposited.


Cheers
Stuart
Stuart both were analytical grades (eg pure Al we use for experiments not an alloy). Like you we also get rid of excess Na metal in 2-propanol for the same reasons and yes the reaction is very slow. I cleaned the Al surface with emery then steelwool and plunged it straight into the alcohol. The sheen of the Al dulled mildly after about 10 mins. Obviously acid or hydroxide will damage the coating with ease (the hydroxide will etch the glass of the mirror as well if it is of a high enough molarity) so best to keep these well away. As for the mirror coating being AlO3 I am unsure. From what I have read on mirror coating it is only possible to achieve the quality required in a vacuum chamber which is evacuated then the Al atomised to form the coat. In any case I would not put alcohols near the mirror sticking to de-ionised water and a mild detergent in the worst cases. Like you my initial thought on this was the 2-propanol must have been contaminated but I am not so sure after mucking around today. I am not excluding dissolved oxygen but I have never seen this happen using good old detergent and de-ionised water and think it's better to be safe then sorry.

Mark

Last edited by marki; 04-11-2009 at 10:12 PM.
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  #28  
Old 04-11-2009, 10:03 PM
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Quote:
Originally Posted by Bassnut View Post
How about Windex?. I tried it once, and it gave a very clean, streak free finish, better than anything else I have tried. Worried me a bit though, there is no mention of chemicals used, but the instructions say dont use on acrylic,fiberglass,painted surfaces, waxed, polished or varnished wood, or tinted windows. What do you think would be in it?, would it damage Al coatings?.
Fred I would not put windex anywhere near your mirror. It often has impurities that cause streaking. You can filter these out some what through high grade filter paper but still.... Ammonia in water forms hydroxide and this can attack the ali and etch the glass. It will only be about 3% ammonia but still not necessary when detergent and de-ionised water can do the job without risk.

Mark

Last edited by marki; 04-11-2009 at 10:28 PM.
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  #29  
Old 04-11-2009, 10:08 PM
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Quote:
Originally Posted by rat156 View Post
Geez, I'd hate to take you to a petrol station...

Petrol
- extremely flammable, forms explosive mixtures with air readily
- nasty in your eyes, on your skin (especially in those sensitive areas)
- don't want to breath in too much
- until recently actually contained a heavy metal poison (Lead)
- until recently contained a confirmed carcinogen (benzene)
- contains CNS toxins (Xylene and Toluene)

Amounts in use, IPA about 125 ml, Petrol usually over 40 litres...

Cheers
Stuart
Maybe I should switch to selling petrol. Gov safety regs now force we lab rats to have to read and signed off on MSDSs for up to 100 substances a year. Sniffing petrol might be easier......
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  #30  
Old 04-11-2009, 10:17 PM
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Originally Posted by RobF View Post
Maybe I should switch to selling petrol. Gov safety regs now force we lab rats to have to read and signed off on MSDSs for up to 100 substances a year. Sniffing petrol might be easier......
I have to read the MSDS sheets and a danger report prepared by the lab tech then sign off for each bloody experiment we do in class. Lets see, 2 x year 12 chem classes, 2 x year 11 chem classes then there's years 8 - 10 AAAAAARRRRRRGGGGGGHHHHH. The poor tech is pulling her hair out. She has spent most of the year preparing the reports . We were using toluene, cyclohexene and cyclohexane as well as bromine water today (fresh and fumming, I tell the kids it will kill thier libido, they don't want to go near it) . This was the first organics lab with my 11's. Even though most work was done in the fume hood there was a lot of broken glassware and several stoned kids. Some of my brightest and most responsible students regressed to the kindy sandpit.


Mark
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  #31  
Old 04-11-2009, 11:06 PM
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Some phrases from the MSDS of the things I work with on a daily basis...

  • Extremely hazardous material. Known human carcinogen. May be fatal if inhaled, swallowed or absorbed through the skin. Causes severe burns. May cause serious eye and lung damage.
  • Toxicity data
    ORL-RAT LD50 2.4 mg kg-1
    ORL-MUS LD50 8.1 mg kg-1
    SKN-RAT LD50 1.7 mg kg-1
  • Highly toxic if swallowed, inhaled or absorbed through the skin. Exposure to even small amounts may be fatal. Readily absorbed through the skin.
  • Vapor (Inhalation/Ocular)
    ECt50 (Mild) = 0.1 mg-min/m3

    ECt50 (Severe) 2 = 10 mg-min/m3

    LCt50 = 15 mg-min/m3

    Vapor (Percutaneous)

    ECt50 (Threshold) 5 = 10 mg-min/m3

    ECt50 (Severe) 2 = 25 mg-min/m3

    Liquid (Percutaneous)

    ED50 = 2 mg/70 kg man

    LD50 = 5 mg/70 kg man

    LCt50 = 150 mg-min/m3
We don't have broken glassware. You want to see the risk assessments...

Cheers
Stuart
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  #32  
Old 05-11-2009, 12:46 AM
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Quote:
Originally Posted by rat156 View Post
Some phrases from the MSDS of the things I work with on a daily basis...

  • Extremely hazardous material. Known human carcinogen. May be fatal if inhaled, swallowed or absorbed through the skin. Causes severe burns. May cause serious eye and lung damage.
  • Toxicity data
    ORL-RAT LD50 2.4 mg kg-1
    ORL-MUS LD50 8.1 mg kg-1
    SKN-RAT LD50 1.7 mg kg-1
  • Highly toxic if swallowed, inhaled or absorbed through the skin. Exposure to even small amounts may be fatal. Readily absorbed through the skin.
  • Vapor (Inhalation/Ocular)
    ECt50 (Mild) = 0.1 mg-min/m3
    ECt50 (Severe) 2 = 10 mg-min/m3
    LCt50 = 15 mg-min/m3
    Vapor (Percutaneous)
    ECt50 (Threshold) 5 = 10 mg-min/m3
    ECt50 (Severe) 2 = 25 mg-min/m3
    Liquid (Percutaneous)
    ED50 = 2 mg/70 kg man
    LD50 = 5 mg/70 kg man
    LCt50 = 150 mg-min/m3
We don't have broken glassware. You want to see the risk assessments...

Cheers
Stuart
Been there, done that, chickened out coz I like living . Can send you some students to test some of those chemicals on if you ever doubt the validity of the MSDS sheets .

Mark
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  #33  
Old 05-11-2009, 06:20 AM
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Already been tested on humans by the Germans and Iraqis
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  #34  
Old 05-11-2009, 07:08 AM
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Isopropyl is a standard for removing greasy deposits on aluminium /overcoated coatings and antireflective thin film coatings. I've found the usual routine of cleaning first with wads of cotton wool and warm dilute water before distilled rinse, isn't enough to get rid of a very tenacious greasy layer on mirrors cuased my air pollution and Eucalyptus oil if you live near the bush, so isopropyl is needed.

The standard test for cleanliness of an aluminium coating is to breathe on it and look out the breath pattern . If it is featurless and even then the coating is clean. if it is spotty and blotchy with big dark spheres then you have an oily deposit. I find that with a clean mirror displaying some greasy deposit even after a standard clean and isoproply , that a buffing with cotton wool and just the moisture of solid breath gives enough action to lift it. There is no danger of scratching the overcoat ( which is as hard as glass) so long as your materials are clean, and only a contamination that is Silica like will be hard enough to cause scratches.

I disagree with one poster that many modern optics are not over-coated. Unprotected aluminum surfaces will look noticeably dull after 6 months of oxidisation and do not cut it in the commercial world. I would say that uncoated surfaces these days would be extremely rare, although there is one aluminisation service in Australia that does not do it.
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  #35  
Old 05-11-2009, 07:44 AM
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Hi Mark, is acetone ok as well?
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  #36  
Old 05-11-2009, 09:18 AM
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Hi Mark, is acetone ok as well?
Hi Marc

I have read that acetone can attack (melt!) certain plastics so if this is the case, Id be very wary about using it!

Cheers

Dennis
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  #37  
Old 05-11-2009, 09:23 AM
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Hi Marc

I have read that acetone can attack (melt!) certain plastics so if this is the case, Id be very wary about using it!

Cheers

Dennis
Sure does but I found it very effective at spot drying (water marks) on mirrors with coton.
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  #38  
Old 05-11-2009, 09:25 AM
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I used to use Acetone to clean acrylic sign panels. I have also cleaned a Achromat doublet with it. I had a web page with instructions I found.(Analytical scientific LTD)
BEWARE ! as Mark said it can dissolve some plastics.
http://www.analyticalsci.com/Astrono...telescope_.htm
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  #39  
Old 05-11-2009, 09:29 AM
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no worries - thanks for the tips.
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  #40  
Old 05-11-2009, 07:31 PM
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Marc acetone (propanone) should be OK. It is a good solvent and cleans well. It should not affect the Al mirror surface or the glass but I would check on the coatings. I suspect these would be reasonably inert in any case. As has been mentioned it can dissolve some types of plastics so contact should be avoided. I wonder how diethyl ether would go? Might try that out on an old mirror.

Mark
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