Cleaning primary: is deionised water ok?

[BrendanC]

Hi all,

So it looks like an insect may have met an untimely death on my primary. There's a small splodge, and it's noticeable on my subs, so I need to clean it.

I've only ever cleaned a primary once before so I'm a bit scared.

I know how to do it, but the question is as per the title: for rinsing it, I see deionised water for sale everywhere, but distilled water seems much harder to find. Is distilled water an absolute must, or would deionised water be ok?

Thanks, Brendan

[PeterCPC]

No you should use distilled - I got mine on Amazon.

[pete_l]

21 minutes ago, BrendanC said:

Is distilled water an absolute must

You will not leave any liquid on the mirror after cleaning - you will dry it thoroughly by absorbtion onto a tissue or somesuch. And with no liquid left on the mirror, there will be nothing to evaporate and leave a deposit.

[callisto]

5 minutes ago, pete_l said:

you will dry it thoroughly by absorbtion onto a tissue or somesuch

I thought you just left the mirror to dry naturally?

[pete_l]

11 minutes ago, callisto said:

I thought you just left the mirror to dry naturally?

I never do and the 20+ year old mirror on my SCT is as clean as when it was new. The secret is to dab, not wipe.
And remember the OP is only talking about cleaning a "small splodge" on their mirror. A single cotton bud will be sufficient.

Edited January 25, 2021 by pete_l

[BrendanC]

I'd probably be cleaning the whole mirror while I'm at it.

I've ordered distilled water just to be on the safe side, and then I think I'll probably try the 'no touch' method by letting it mostly dry on its own then using a hairdryer to get any excess off.

[callisto]

5 minutes ago, pete_l said:

I never do and the 20+ year old mirror on my SCT is as clean as when it was new. The secret is to dab, not wipe.
And remember the OP is only talking about cleaning a "small splodge" on their mirror. A single cotton bud will be sufficient.

Yeah, I understand what you mean but when I clean my mirror in the sink I gently use one cotton pad for each wipe over the mirror, put mirror in its side and pour distilled water over to rinse and leave to dry....well that's the way I do it anyway

[pete_l]

17 minutes ago, callisto said:

one cotton pad for each wipe

Be aware that cotton buds are abrasive. That is why they are useful for cleaning metallic contacts on switches and connectors. Printer paper is another good material for cleaning contacts, because it is abrasive, too.
 

As regards contaminants in water. Hard tap water is unlikely to contain more than 300mg of "stuff" per litre. A single drop of water 1mm³  is one-millionth of a litre. So the maximum amount of minerals in that amount of tap water is 3x10-11 grams In comparison, a single speck of dust is 3000 times larger.

Even that amount in tap water is negligible. In deionised water there are typically 100-1000 times less contaminants. So even with that, the amount of impurities are too small to measure.

So if used properly and dried-off correctly, any sort of water will leave a mirror or lens free from surface dirt.

Edited January 25, 2021 by pete_l

[callisto]

10 minutes ago, pete_l said:

Be aware that cotton buds are abrasive

I don't use cotton buds....I use medical cotton balls like these-   https://www.reliancemedical.co.uk/product/cotton-wool-bp/