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Old 02-11-2009, 10:50 AM
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pmrid (Peter)
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Isopropyl Alcohol as a lens/mirror cleaner or dissolver of optical coatings

What are your thoughts about this. I was about to embark upon a morning chore of removing the dust motes and other bits of whatever that seems to end up on glass surfaces and imaging chips. I'd seen somewhere in these forums a reference to isoptopyl alcohol as the cleaner of choice for this sort of job. The only form of this stuff my chemist could supply was a 65% solution (it didn't say what the other 35% was) under the brand name isocol. I wasn't entirely comfiortable - not knowing what that other 35% was and being concerned about the effect of this stuff on coated optics.

So I dragged out a couple of old/cheap eyepieces and used them as a test.

When I had smeared some of this across the surface of a coated eyepiece with a bit of cotton wool, I had a look at that surface under a magnifying glass: it seemed to me that the alcohol had dissolved/melted the coating. That was the end of that experiment and the beginning of this thread. Before I go any further with the CCD's can you tell me what you use for cleaning glass elements in your imaging train, and CCDs in particular.

Peter.
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Old 02-11-2009, 11:02 AM
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70% isopropanol - 30%double distilled water.
Nothing else.
You may have just partially removed years of grease build up from eyelashes rather than any coating.
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Old 02-11-2009, 06:13 PM
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Some time ago I purchased some 99% IPA from the Chemist – I had to show him my book on cleaning optics before he would sell it to me, for fear of misuse.

I think that anything less than 99% proof “may” be contaminated with other additives. IIRC, one post on sci.astro mentioned that some sort of oil was added to cheaper solutions and this would leave a film after the alcohol had evaporated.

The above comments are made up mostly of memory recollections and is not qualified advice, just a warning to check!

Cheers

Dennis
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Old 02-11-2009, 07:12 PM
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some isopropyl alcohol sold in chemist/pharmacy os really mouth wash & can have additives. Luckily i work in school & know i am using 99% proof watered with distilled - this liquid combo should be safe to use on all optical surfaces.
A chemical company can sell you the good stuff so to speak
Sometimes acetone (nail polish remover) is a stronger solvent - (we used to use it to remove urine from our microscopes)but it is possible it could damage/degrade some coatings or plastic parts near glass surfaces. Always wash it well off with water.
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Old 02-11-2009, 07:21 PM
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Quote:
Originally Posted by dannat View Post
some isopropyl alcohol sold in chemist/pharmacy os really mouth wash & can have additives. Luckily i work in school & know i am using 99% proof watered with distilled - this liquid combo should be safe to use on all optical surfaces.
A chemical company can sell you the good stuff so to speak
Sometimes acetone (nail polish remover) is a stronger solvent - (we used to use it to remove urine from our microscopes)but it is possible it could damage/degrade some coatings or plastic parts near glass surfaces. Always wash it well off with water.
Daniel. I am absolutely not going to ask about the microscopes... Honest, I'm not. No, really!!!
Peter
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Old 02-11-2009, 07:48 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
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Old 02-11-2009, 08:03 PM
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Peter, I would ask the Chemist to order in the 99% for you. It is not cheap, from memory $35 for 0.5 L but it is the good stuff. It is available but usually only by order.
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Old 02-11-2009, 11:40 PM
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I got hold of some diggers isopropyl alcohol from bunnings tonight and sprayed it on plastic and then hit it with a hair dryer and it completely evaporated, quick smart. I did the same with some isocol and was left with lots of water droplets after hitting it with the hair dryer. It looks like diggers will do it, $11.70 for 125ml.
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Old 03-11-2009, 07:59 AM
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I don't know if I'd use Isopropyl on optics... I definitely think its great for cleaning camera sensors, but I would be wary of touching mirrors or APO telescope lenses with it... tiny dust spots on a telescope lens will go unnoticed in both visual and photographic use, and by cleaning it all you are doing is risking the optical integrity of the telescope... most of the dust motes you see in images will be dust or specs of something on the sensor or on the filters, and its usually fairly easy to tell which is which based on the intensity of the mote in a flat frame. With your QHY8, its easy enough to open the camera up, clean the sensor and the optical window then seal it back up, and I think thats worth doing (I used to do mine once a month)

On the Astro-Physics website, Roland has a bit of an article covering his thoughts on cleaning refractor lenses.. Summarized, he basically says that until you notice it visually, do not touch it. and once you do notice it, get it professionally cleaned by someone who knows what they are doing..
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Old 03-11-2009, 09:28 AM
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Not sure about your scope optics Alex but it is the only cleaner recommended by meade for their UHTC coatings. Robin it doesnt hurt to dilute the alcohol with some deionised water. Cleans well and leaves no marks.

Mark
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  #11  
Old 03-11-2009, 10:10 PM
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Wary about using isopropyl alcohol on aluminium mirrors

I have a sense that isopropyl alcohol reacts with aluminium, so would be wary about using it for mirror cleaning. There is some chemistry here that I don't understand, but when I used it once I was convinced that it left streaks that did not dissolve in distilled water.

Would be interested to hear from a chemist on this.
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Old 03-11-2009, 10:42 PM
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Quote:
Originally Posted by Andrew C View Post
I have a sense that isopropyl alcohol reacts with aluminium, so would be wary about using it for mirror cleaning. There is some chemistry here that I don't understand, but when I used it once I was convinced that it left streaks that did not dissolve in distilled water.

Would be interested to hear from a chemist on this.
You will have to let me have a think about that one as it is a secondary alcohol which are not that reactive to start with (could be wrong will check). In any case I would not be using anything but de-ionised water and mild detergent to clean your mirror.

Mark

Last edited by marki; 03-11-2009 at 11:07 PM.
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  #13  
Old 03-11-2009, 10:50 PM
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Update from the MSDS datasheet. Seems your hunch is correct.

10. Stability and Reactivity
Stability:
Stable under ordinary conditions of use and storage. Heat and sunlight can contribute to instability.
Hazardous Decomposition Products:
Carbon dioxide and carbon monoxide may form when heated to decomposition.
Hazardous Polymerization:
Will not occur.
Incompatibilities:
Heat, flame, strong oxidizers, acetaldehyde, acids, chlorine, ethylene oxide, hydrogen-palladium combination, hydrogen peroxide-sulfuric acid combination, potassium tert-butoxide, hypochlorous acid, isocyanates, nitroform, phosgene, aluminum, oleum and perchloric acid.
Conditions to Avoid:
Heat, flames, ignition sources and incompatibles.

Appears it does the same as a primary alcohol with sodium metal and forms a Al salt (aluminium isopropoxide). The hydrogen is knocked of the hydroxy group and forms hydrogen gas, The Al dissolves forms a salt.

Mark

Last edited by marki; 03-11-2009 at 11:10 PM.
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Old 03-11-2009, 11:04 PM
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Yes, a similar problem to Aluminium car engine parts and Ethanol fuels.
Quote:
Originally Posted by marki View Post
Update from the MSDS datasheet. Seems your hunch is correct.

10. Stability and Reactivity
Stability:
Stable under ordinary conditions of use and storage. Heat and sunlight can contribute to instability.
Hazardous Decomposition Products:
Carbon dioxide and carbon monoxide may form when heated to decomposition.
Hazardous Polymerization:
Will not occur.
Incompatibilities:
Heat, flame, strong oxidizers, acetaldehyde, acids, chlorine, ethylene oxide, hydrogen-palladium combination, hydrogen peroxide-sulfuric acid combination, potassium tert-butoxide, hypochlorous acid, isocyanates, nitroform, phosgene, aluminum, oleum and perchloric acid.
Conditions to Avoid:
Heat, flames, ignition sources and incompatibles.

Mark
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Old 04-11-2009, 09:08 AM
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Quote:
Originally Posted by Andrew C View Post
I have a sense that isopropyl alcohol reacts with aluminium, so would be wary about using it for mirror cleaning. There is some chemistry here that I don't understand, but when I used it once I was convinced that it left streaks that did not dissolve in distilled water.

Would be interested to hear from a chemist on this.
Highly unlikely, there was probably some impurity in the alcohol used. Isopropanol will evaporate with no residue. Remember your coating is NOT aluminium but aluminium oxide, an enert unreactive matrial. Powdered aluminium or even metalic is different.
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Old 04-11-2009, 09:33 AM
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Quote:
Originally Posted by allan gould View Post
Highly unlikely, there was probably some impurity in the alcohol used. Isopropanol will evaporate with no residue. Remember your coating is NOT aluminium but aluminium oxide, an enert unreactive matrial. Powdered aluminium or even metalic is different.
Allan, I very much doubt the mirror has an AlO3 coating. MgF2 or SiO2 yes.

Mark
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Old 04-11-2009, 09:59 AM
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Quote:
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Allan, I very much doubt the mirror has an AlO3 coating. MgF2 or SiO2 yes.

Mark
Still the point is, neither/none of them is Aluminium.
We use isopropanol every day and reactivity with Aluminium is not one of our concerns.
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Old 04-11-2009, 10:52 AM
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I've used Isopropyl for years without any damage to lens coatings; on occasions I also use Acetone to remove stubborn deposits that aren't removed by Isopropyl (need to not let acetone touch anything other than the glass). It's better to disolve a deposit with acetone than to rub hard with Isopropyl.

Eyelash oil on eyepieces should be removed as soon as possible. Objective lenses that get dewed should be cleaned occasionally since contaminants in the atmosphere damage coatings. All IMHO.
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Old 04-11-2009, 10:57 AM
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Just a thought [Satchmo] would know that. He's a mirror maker. Hear it from the horse's mouth.
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  #20  
Old 04-11-2009, 12:05 PM
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Quote:
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Allan, I very much doubt the mirror has an AlO3 coating. MgF2 or SiO2 yes.

Mark
Actually raw Aluminium converts to the oxide faster than you can blink. The surface of almost all aluminium is coated in the oxide as soon as it's exposed to air. So it is possible that it is coated in Al oxide. Some mirror manufacturers coat with SiO2 after the deposition which is done in an atmosphere devoid of oxygen (and all other gasses). Most don't though.

Cheers
Stuart
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