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Spray Silvering how-to pages are up

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111 replies to this topic

#101 radicell2

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Posted 09 December 2019 - 09:48 AM

IIRC, both talcum powder and CC are softer than glass and therefore do not affect the figure at all.

There was mention that the figure isn't changed by spray-silvering - think an interferometer was used to look at the surface.Question of degree of change

But having seen how random the Youtube video shows the technique of using spray bottles to impart the silver and the muscle cramps in the hands,I'd be hard pressed not to think that the figure has been changed.Not grossly but many more hills and dips than on a clean surface.

 

Ric



#102 Bob4BVM

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Posted 09 December 2019 - 01:56 PM

You're thinking of it like a coat of paint, it's not like that at all...


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#103 totvos

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Posted 09 December 2019 - 02:04 PM

There was mention that the figure isn't changed by spray-silvering - think an interferometer was used to look at the surface.Question of degree of change

But having seen how random the Youtube video shows the technique of using spray bottles to impart the silver and the muscle cramps in the hands,I'd be hard pressed not to think that the figure has been changed.Not grossly but many more hills and dips than on a clean surface.

 

Ric

The tin solution bonds to the glass, atomically, and the silver bonds to the tin, atomically. This is not painting silver onto the surface and spraying more silver solution onto the prepared surface merely wastes silver. Anything not bonded just washes off.


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#104 Chomatic Aberrant

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Posted 09 December 2019 - 04:02 PM

Question:  I've always used Hydrochloric acid (muriatic acid) to strip aluminum or beral coatings from mirrors.  Should I not? 

 

C.A.



#105 Bob4BVM

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Posted 10 December 2019 - 04:58 PM

Ferric chloride (FeCl) works fine on Al coatings, pretty mundane stuff, a lot less nasty than HCl

Easy to find, it is the old standard PCB-etching chemical

Not sure how it'd do on beral, but easily dissolves Al and Cu



#106 Oregon-raybender

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Posted 10 December 2019 - 07:14 PM

Chalk or silver coating will not change or effect the optical surface. I used both on hundreds of precision optics at Tinsley and other optical companies. The silver coating was used to enhance the fringes while testing using interferometers. I coated optics from 2 inches to 36 inches. As stated the chalk is used to produce a very clean surface for the tin/silver to attach to with out staining. Cleaning the edges is key. Green River (a mix of muriatic acid, water and copper sulfate) was used to remove the silver coating.

See old forums on CN, I and others have mention it.

 

 

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#107 Chomatic Aberrant

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Posted 10 December 2019 - 09:26 PM

I have found many uses for Muriatic acid.  Why, I'd use it for brushing my teeth, if I could. (just kidding)  My 12.5 mirror fit firmly at the bottom of my poly-whateverthylene laundry sink in the basement.  Had no problems.

 

Robert.

 

Just curious. Outside of the color change what other reason(s) did Green River have to add Copper Sulfate to their mirror stripper?  Copper Sulfate is found in every hardware store here in Illinois. We dump it down the drain every spring to fight off tree root penetration under the front yard.

 

(And here I thought Green River was only the soft drink I drank as a kid at the soda fountain. )   C. A.



#108 Oregon-raybender

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Posted 11 December 2019 - 01:39 PM

The question about adding copper to the mix is one for the chemists in the group to explain. I know that Green River works really well and IMHO easy to use following the safety requirements.

 

But, as always read, understand and follow the SDS handling requirements, safety first in mixing and handling ANY chemical, PPE is always needed and the right area to mix. Protect your shelf and others.

 

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#109 junkbum35

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Posted 29 December 2019 - 08:28 PM

I use HCl mixed with copper (II) nitrate to remove old aluminum coatings. It's nasty (and will oxidize any iron in the vicinity) but I think it works a bit faster than ferric chloride. I've used both precipitated calcium carbonate AND Alconox to clean mirrors. Probably best to use both in this process. I suspect the cleanliness requirements are stricter for chemical deposition than they are for vacuum deposition.

 

By the way, vacuum deposited Al will stay on your mirror for many years (unless you live in an environment with nasty air). But the maximum reflectivity of aluminum, enhanced or not, is about 10 percentage points lower than that of silver. The coatings we put on mirrors up to 12.5" here in DC at our ATM workshop have rather smooth finishes at the atomic level, according to electron micrographs a very nice professional did for us. We don't have the ability to overcoat.

 

Got a 16.5" mirror that I'm still working on; hope to use the process demoed at Stellafane this summer by Peter Pekurar of precipitated, sprayed, overcoated Ag, described here.


Edited by junkbum35, 29 December 2019 - 08:33 PM.


#110 junkbum35

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Posted 29 December 2019 - 09:36 PM

Thanks for sharing this information!

Guy



#111 Mike Spooner

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Posted 30 December 2019 - 09:43 AM

Ferric chloride works well on aluminum and Beral. Won't touch chromium base. It doesn't work well at all if too cool in my experience. I like using it at 90 degree F. Stripped a 36" spray silvered mirror in short order (October in Arizona so it was toasty)smile.gif.

 

The "spray" silver process worked for us the one time we used it. Easier than I had hoped for and good result. 

 

 

Mike Spooner 


Edited by Mike Spooner, 30 December 2019 - 09:45 AM.

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#112 Craig F. McCaw

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Posted 21 March 2021 - 12:05 AM

A couple of questions if I may.

 

I have a 17.5",  a 1971 Cave 8", and a couple of 4.5" flats with Spectrum enhanced coatings done in 2006.  The pinhole police say that it's time to start to think about re-coating at some point, and the spray silvering concept looks really interesting. I could share it with some other folks ( 25 inch, 18 inch) that also need to do some re-coating.

 

I live right on the ocean in Vancouver BC on the Wet Coast and the rolloff gets really humid some mornings. The 17 has a reptile heater pad behind, and an infrared heat bulb on the front, on timers, and they seem to keep the mirror dry in the mornings. The heat lamp trick worked at the DAO when they couldn't keep a coating on the 48".

 

I was wondering if there were any updates on the Midas "overcoat" protection.

 

As the spray process seems to require fresh air, or at least an open garage door, I was wondering if Rigid Collodion might work for the pre-cleaning process.  Over the years I have used it on a bunch of mirrors, and stuff looks just like it came out of the coating chamber afterwords. The alcohol and ether would certainly de-grease the surface and the cellulose would entrap any particulates. It's nasty stuff but if it's outside with a breeze it's fine. I've never had any problems with it all coming off, just paint it on in  thick layers and it evaporates so quickly the cooling effect causes the top layer to contract and I could just watch as it peeled itself off the mirror.

 

The movie SFX industry has a version that's cheaper than the medical/scientific grade that works well on optics.

 

Certainly If it ain't broke don't fix it, and the standard cleaning process seems to be great, but I was just wondering if anyone had given it a try.

 

Thanks,

 

Craig




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