Removing mirror’s coating

Frankenscope? Let's see it!***be advised that NOTHING in this forum has been safety tested and you are reading and using these posts at your own peril. blah, blah, blah... dont mess around with your eyesight when it comes to solar astronomy. Use appropriate filtration at all times...
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allhoest
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Removing mirror’s coating

Post by allhoest »

The purpose of the present operation is to remove the aluminum coating, for use in solar observation.

Warning: the following manipulations involve corrosive products. It is your responsibility to take the necessary protective measures.

Warning: solar observation can be dangerous if it is not practiced with care. It is your responsibility to master your observation technique. Do not take any risk.

It is also necessary to collect corrosive products after using to eliminate them (if necessary) according to the rules.



Here is the mirror, the victim.
Image




It will be packed, the purpose being to limit the amount of corrosive agent used to treat the mirror.
Image




The product used is iron perchloride. It is widely used in electronics to remove surplus copper on printed circuit boards.
It is also effective on aluminum removal.
If the mirror packaging is tight, then a limited quantity is sufficient.
Image




The process begins immediately at the weakest areas, for example those with scratches.
Image




The process that started quickly, has finally proved to be quite slow. Here after 6 hours of treatment.
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The next day, after ~ 18 hours of treatment, untreated areas are still visible.
Most surprising is this matte layer on the surface of the mirror. It would be a primary adhesion, explaining the slow treatment.
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This primary layer will be largely taken out during a rinsing with JETS of distilled water. But bright spots persist, as well as traces of this adhesion product.
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To remedy this, the process takes a new phase, here with hydrochloric acid.
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The process is slow; after several hours, bright dots persist.
Image




After 24 hours of acid treatment, the mirror is rinsed with distilled water.
Image




The mirror is finally operational, for a new life.
Image







Alex
2019-Aug-17


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Re: Removing mirror’s coating

Post by marktownley »

Great step by step Alex that looks to be producing excellent results!


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Re: Removing mirror’s coating

Post by Carbon60 »

Good to know, Alex. As you say, anyone doing this should take all necessary precautions. I work in the chemicals (polymer) industry. For this type of work our guys in the lab would wear acid resistant gloves (thicker and longer up the arms than the ones you used) a full face visor and a protective apron over a lab coat.

Ensure there is a supply of water close by to wash away any acid that gets on your skin and ensure that spills are neutralised and washed away.

So, again, to anyone thinking of doing this, I cannot stress enough the dangers of using highly corrosive substances. Apologies if this message appears overly cautious, but I’ve seen the results of acid burns. They can be deep and life changing. Use with caution and respect!

Stu.


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Re: Removing mirror’s coating

Post by christian viladrich »

Hello STu,
Thanks a lot for your input.
Could you tell us a little bit about the differences between iron perchloride et HCl ? I understood than the first one is less agressive ?


Christian Viladrich
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Editor of "Solar Astronomy"
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Re: Removing mirror’s coating

Post by Carbon60 »

Hi Christian,

Not an easy question to answer, as it depends on the concentrations of either substance.

Material Safety information can be found here:

https://pubchem.ncbi.nlm.nih.gov/compou ... _-chloride

https://pubchem.ncbi.nlm.nih.gov/compound/313

Both are corrosive, causing skin and eye damage and Iron III Chloride (Iron Perchloride) is toxic.

In either case, best to use caution.

Stu.


H-alpha, WL and Ca II K imaging kit for various image scales.
Fluxgate Magnetometers (1s and 150s Cadence).
Radio meteor detector.
More images at http://www.flickr.com/photos/solarcarbon60/
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Re: Removing mirror’s coating

Post by bart1805 »

I used ferric chloride (40%) for my mirror. Professionals seem to use a solution called green river:
"Green river is a solution consisting of two quarts of distilled water, one quart of hydrochloric acid, and one ounce cupric sulfate."


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Re: Removing mirror’s coating

Post by marktownley »

I think i'll leave this post here in the mods to pick up and remaining comments / discussion on the thread, and then move to the solar library as is a great resource.


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