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Distilled vs deionised water


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Hi,

I'm unfortunately needing to clean my primary mirror on my 8" newtonian. It's not been used for several years and unfortunately has a considerable dust build up inside despite being sealed at both ends. 

I've been investigating what kit is needed and all the precautions about scratching the mirror etc, but there is one thing I'm not sure of. The guides all say to use distilled water yet this doesn't seem to be readily available locally. Everywhere I look has deionised water. I know they are different but is there any practical difference when it comes to using either for rinsing the mirror off? 

Thanks

Ed

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Frankly I'm sceptical.  I think it unlikely that contaminants in deionised water will be present at sufficiently high concentrations to damage or corrode the mirror surface, or indeed to significantly

Deep sigh putting on 'work' hat. Distilled water is an outdated method of producing 'purified' water of no specific classification. Type 3 water, RO, basic DI and filtration, has a resistivi

Sounds a bit fishy to me       

I am happy to be corrected, but I would suggest that either distilled or deionised water would be fine.  What you want is to ensure that you have minimal deposits left on the mirror after rinsing.  If you live in a hard water area, you will be aware of these from your shower or kettle.

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24 minutes ago, laudropb said:
24 minutes ago, laudropb said:

Distilled is the better option. There are less impurities in it.

 

In general I would disagree with this statement.  I work in for a "scientific" company and our DI water system will give you water far purer that distilled water.  Having said that, distilled water will be fine for cleaning a lens, not sure that I would say the same for a CCD sensor :)

Edited by davedownsouth
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I stick by my first statement. I worked in a laboratory for more than 40 years. When cleaning glass to be used for cell culture the last rinse was always in distilled .water. Deionised water from its name removes charged particles, but has no effect on uncharged impurities

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I work for a company that makes ultra pure water systems. Modern DI water will be fine since it will also have gone through activated carbon treatment and several levels of filtration. Anything that says type II water will be fine.

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RO (reverse oscillation) Distilled Marine (poss typeIII) available through aquariums such as found at Garden Centres. From there you can purchase a 5L water carrier which just get refilled, last two occasions I'd cleaned mirrors, I got the water for free. 

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I've seen various types/grades for sale on the web, but I'm never completely sure that they correspond to the quality I have used in the "day job" for ultra-trace analysis - I therefore check whether water is pure enough to use for optics cleaning by making a little pool of it in the centre of a magnifying shaving mirror, and leaving it somewhere for the water to evaporate; there should be no deposit or "rings" visible. 

Chris

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10 minutes ago, chiltonstar said:

I've seen various types/grades for sale on the web, but I'm never completely sure that they correspond to the quality I have used in the "day job" for ultra-trace analysis - I therefore check whether water is pure enough to use for optics cleaning by making a little pool of it in the centre of a magnifying shaving mirror, and leaving it somewhere for the water to evaporate; there should be no deposit or "rings" visible. 

Chris

Exactly, if it evaporates with no trace, that is good enough.  A better test would be to put a drop onto you CCD sensor, leave it to evaporate (in a clean air filtered environment), and then take a Flat.  If you see nothing, it is good water.  NB.  No body in their right mind would actually do this :tongue2:

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56 minutes ago, Physopto said:

I think you mean reverse osmosis, as I have never heard of reverse oscillation?

I am always willing to learn though.  :)

Derek

 

Yes, the system we have at work is two carbon filters / followed by three RO units / followed by three DI units and finally Ultrafiltration.  You are not going to see any residual after all this :biggrin:

Edited by davedownsouth
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I'm an organic-chemist. And have taught chemistry in high-school - from when I was 15 years old. I rather know my way around chemicals. If I didn't, I'd be in the ionosphere! Regards distilled water - this is what you want. Triple-distilled, if the store has it, is the best grade. But distilled regardless. "Deionized" means it shouldn't have minerals in it. But that leaves a lot of territory for all sorts of other things - like chlorine and whatever else was blowing in the wind that day. Distilled means it has been boiled, the steam condensed back into liquid H2O through a condenser, and collected in a separate vessel.

Get distilled - if you want nothing left on your mirror, lens, whatever you're cleaning.

Dave

 

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Distilled in my book. After cleaning and a final rinse I lay the mirror on a towel angled on it's side and gently blow dry the excess water off it. Distilled will roll right off and leave no trace.

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I have always used deionised water for the final rinses.   I have cleaned my 200p's mirror five or six times in as many years.  Deionised water appears to have no adverse effect on either the mirror's coating or its reflectivity.  

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I used DI water available from Asda in the car cleaning/accessory area. However, I must admit there were some slight areas of 'deposit' left in the primary when I'd finished. May try  to find distilled next time. 

Edited by kerrylewis
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Would I be right in thinking that distilled is more expensive to make which is why it is less available to buy?  Plus for most applications deionised is satisfactory - filling irons and the like. 

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Deionised water is very good but if it is deionised and distilled it will be better.  I say this as at university we only used that type of water and I was informed long ago that it was considered the best method. I would guess that the deionisation removed the particle contaminants as well as ionised particles. Whilst the distillation removed other chemicals not able to be removed in the deionisation filters.     Dave In Vermont is correct  I am sure in that triple distillation is the best available distillation method/number of treatments. 

When I was at sea many moons ago as part of my job I had to look after the water evaporators. These machines took raw sea water and provided all the fresh water for every one on board ship to drink, wash in and for every other general use that sea water could not be used for. One very important point about this method of providing fresh water is not to push the process too hard. If you do, you can get a carry over of contaminants. So there is a limit to the rate of purification, we had to watch the measured parts per million of the distilled product.  Distilling several times will remove more of the contaminants each distillation. 

No method is perfect, but a combination is probably best if properly and carefully done.

As a side note we all drank distilled water at sea, but drinking distilled water in general is not recomended as the process removes nearly all required minerals needed for a healthy body.

Derek

 

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I think 'it depends' is your answer. Well filtered DI will be ideal, so will good distilled but both methods cost money.

Water that's been shoved through a naff DI unit or a poorly run still will not be good. Remember that most water from Asda or the garage is for car batteries and steam irons - a bit of contaminant will not be noticed by the punters so why purify further? Keep it cheap ...

I run a couple of stills at work and, as long as they are not pushed too hard, the single distillation is perfectly good enough for cleaning mirrors. I think the deliberately added impurities are potentially worse - scratchy cotton wool, alkali in 'fairy liquid', dirty microfibre cloths ... Mechanical care is far more important as, ideally, the water will sheet off a clean mirror anyway so contamination will be minimal.

AndyG

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