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Spray Silvering how-to pages are up

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#26 Bob4BVM

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Posted 15 October 2019 - 02:05 AM

The perfectionist in me needs to point out that Si is silicon, and Ag is silver. ;-)

Ha ha, you got me ! smile.gif  Thx for correcting me, I knew that but sometimes I get sloppy with my abbreviations !  Too used to referring to "Al" in this hobby... caught by a trap of my own making

smile.gif

Bob


Edited by Bob4BVM, 15 October 2019 - 02:07 AM.


#27 Bob4BVM

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Posted 15 October 2019 - 02:15 AM

Thanks Tomo, you just beat me to it!

 

Also, the Midas anti-tarnish overcoat means you don't need to create an oxygen-free environment to slow down tarnishing - that's what the Midas is for. The act of observing with a silver coating on your mirror means other environmental factors will get to the coating no matter how you store the mirror before and after observing.

 

Dust, bugs, pollen and who knows what else floating around in the air will land on the silver coating no matter what. Our best guess is that water vapor in the air is soaked up by these particles while they're on the coating and stuff that degrades silver is dissolved onto the coating and creates small (1 to 4 mm diameter) spots over time. If you observed only in extremely low humidity, with no bugs, this might not be a problem, but who doesn't eventually get a dewy night and a few bugs?

 

Anyway, this is what we hope to prevent with a new overcoat, and if successful it could mean a spray silver coating could become nearly as durable as an aluminum coating. Stay tuned!

Yes, that makes total sense Howard. The danger is when it's open for observing.  Makes me hope that Ed's air system can be built in a way to overcome the contaminants you list above. Perhaps Ed will chime in here and tell us how it is working and if he thinks we can hope for enough of a 'pressurized air column' over the mirror to keep dew and most other contaminants at bay. My thinking is the worst case would be crud getting on a dewed-up mirror surface

Bob



#28 DAVIDG

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Posted 15 October 2019 - 09:12 AM

  Well me too but I just found on the Oregon Scope Werks web site that they used precipitated calcium carbonate and that's not going to have any hard contaminates.  It's a whole lot better than using old school concentrated nitric acid; really nasty stuff.  

  I'm curious what's in the Midas anti-tarnish.  I looked at the MSDS but none of the listed ingredients react with silver.  They did say that some proprietary non-hazardous ingredients may not be listed and I'm betting it's benzotriazole (BZT).  I know about 15 or 20 years ago I posted a pic on CN of a silvered microscope slide half of it dipped in BZT.  I had exposed it to hydrogen sulphide gas and the BZT really did protect it.  Not perfect but necessary.  I hope to see what their other anti-tarnish fix is.

  The other thing with silvered mirrors is to always make a mirror cover to keep dust and other nasties out.  

 

Ed

 Being chemist I looked the MSDS as well and I think I know what is going on.  The Midas anti-tranish uses a couple of different alcohols  and tetrachloroethylene . These are used in  making a super hydrophobic solution of SiO2 nano particles. So what I think is going on is that the solution forms a mono layer of SiO2 over the surface of the mirror which protects it from oxidation. 

 

                 - Dave 


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#29 tommm

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Posted 15 October 2019 - 09:18 AM

I think Ed has already posted that is the case. He stated his mirror is still very clean. His vented mirror box cover would prevent this: The second time I set out my rebuilt scope to cool I came out later to find bird **** on my newly made mirror and coating.  Now I always pull the shroud down to protect it.



#30 phonehome

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Posted 15 October 2019 - 11:09 AM

Yes, that makes total sense Howard. The danger is when it's open for observing.  Makes me hope that Ed's air system can be built in a way to overcome the contaminants you list above. Perhaps Ed will chime in here and tell us how it is working and if he thinks we can hope for enough of a 'pressurized air column' over the mirror to keep dew and most other contaminants at bay. My thinking is the worst case would be crud getting on a dewed-up mirror surface

Bob

 

Bob,

 

I don't want to "contaminate" this thread [pun intended] but yes the "Elvira system" as you say could be most helpful with this [currently] sensitive Ag coating.

 

Among other things it effectively stops dust, pollen, insect, etc. contamination when covered/stored or venting/acclimating and significantly reduces it when uncovered/observing.  It minimizes electrostatic attraction of particles from airflow and it stops condensation [both dew and frost] on the primary and secondary when implemented and utilized as recommended.  This includes bringing a cold mirror into a warm/humid space that usually results in condensation.

 

So it is possible to at least remove condensation as a destructive mechanism on this [or any other] coating while storing, acclimating and observing.

 

Maybe the Oregon Scope Werks at some point could investigate and quantify this further... 

 

Ed


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#31 mconnelley

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Posted 15 October 2019 - 01:14 PM

Hello:

   

  As someone who does live on the Big Island with a (recently) very active volcano, I'm been reading this thread with some interest.  One thing that hasn't been mentioned much is the effect of condensation on the mirror.  For example, I live in warm tropical Hilo, but our observing site is up above 9000 ft. to get above the clouds.  The telescope gets nice and cold while we're observing, and dews over on the drive down.  This is inevitable unless you put your whole telescope into an airtight bag on the way down.  Due to the change in air pressure, warm moist air will make its way into the telescope and condense on everything.  A friend of mine had his mirror recoated at Gemini with their protected silver coating.  After one damp night, the coating was ruined.  

Cheers

Mike


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#32 Bob4BVM

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Posted 15 October 2019 - 09:24 PM

Bob,

 

I don't want to "contaminate" this thread [pun intended] but yes the "Elvira system" as you say could be most helpful with this [currently] sensitive Ag coating.

 

Among other things it effectively stops dust, pollen, insect, etc. contamination when covered/stored or venting/acclimating and significantly reduces it when uncovered/observing.  It minimizes electrostatic attraction of particles from airflow and it stops condensation [both dew and frost] on the primary and secondary when implemented and utilized as recommended.  This includes bringing a cold mirror into a warm/humid space that usually results in condensation.

 

So it is possible to at least remove condensation as a destructive mechanism on this [or any other] coating while storing, acclimating and observing.

 

Maybe the Oregon Scope Werks at some point could investigate and quantify this further... 

 

Ed

Thanks for affirming the details Ed.

Your system seems a perfect match for a silvered mirror.

I am busy adapting your air system to my binoscope cells... seems the planets are aligning perfectly for me !

CS

Bob



#33 Ed Jones

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Posted 16 October 2019 - 10:35 AM

A good use of silvering is when using an oil flat. Three uncoated reflections makes for a extremely faint image but even a partial silvering would help a lot. Cassegrain and compound designs would be simplified
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#34 Oregon-raybender

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Posted 16 October 2019 - 07:48 PM

Having slivered 100's of optics at Tinsley back in the day. I was the one who suggested using chalk for

cleaning to Oregon group last year. It was used successfully with no issues and provided wonderful sliver

coatings. It was part of the process that I use and others and wrote about over the years for cleaning optics.

 

This method used for decades before me. In 1824, it was used by John Fraunhofer on lenses before

assembly. It is also used by silverers. Cleanliness is the key to get a clear and bright coating, chalk just works.

 

II also suggested the use of "Green River" to remove the silver verses FC. Green River has been successfully on the

200 inch and 120 inch mirrors, as well as many optical coating companies and is easy to use.

 

I think that it is wonderful that the Oregon group has provided this to world. It took the effort of many people who

have skill and willingness to look into cost saving option to ATMer's. I hope this becomes a successful project in

the years ahead.

 

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#35 JohnH

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Posted 16 October 2019 - 09:47 PM

I would like to hear how some ATMs here fare with this method.



#36 sopticals

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Posted 18 October 2019 - 05:57 PM

If you just buy the chemicals and use your own spray bottles  it's around $100 and that will do several mirrors and lasts for years if you put them in the fridge. 

Just like to add my 2c. I have spray silvered a number of mirrors (using the AG chems), 22" to 33". Couple of photo's of 25" , one, when freshly silvered and another of another 25" showing

degradation of an unprotected silver coating after two years of use (and abuse-[drenched with water condensation multiple times]). 

 

Refrigerating the chemicals is a good idea if (if you have the space in your fridge to store such for a long period of time). Outside of refrigeration, storage (if in a consistently cool place) the

life of the AG chems may last 15-18 months. 

 

As Steve has said, you can "gear up" for spraying silver with a few spray bottles from your local garden store.

 

Stephen.(45deg.S.)

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#37 totvos

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Posted 19 October 2019 - 12:32 PM

Stephen, have you tried a PMRT on that heavily used mirror? I'd be curious to know the change in reflectivity (reflectance?) between the two.



#38 Taosmath

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Posted 19 October 2019 - 05:26 PM

Our club has a 30" spray silvered mirror which was coated with ( I believe) BTA photographic developer, and I have two questions:

 

  1. Has anyone any experience with this as a protective layer? - how does it hold up? (after one year the coating looks decent, but not flawless)
  2. How can you remove it & the silver? - we are considering going to a protected aluminum (vacuum deposited) coating and want to clean off the old stuff before we sent it out for recoating.  Should we polish with chalk?  Would the green river/ferric chloride or AG stripper work?

Thanks



#39 Steve Dodds

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Posted 19 October 2019 - 06:02 PM

Silver just wipes off with ferric chloride


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#40 Oregon-raybender

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Posted 20 October 2019 - 09:01 PM

So it does with Green River, but not as messy or brown stains. IMHO. That's why Tinsley, Lick and other

major observatories stopped using FC. But to each it's own.

 

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#41 Taosmath

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Posted 20 October 2019 - 10:14 PM

Yes, I saw above in post #34 that GR will remove the silver, but will it be able to penetrate the developer overcoat?



#42 Oregon-raybender

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Posted 21 October 2019 - 02:31 PM

It should, there are always pin holes in the coating some where, even a SIO2. I would check to see

what does remove the developer overcoat. Could simple soap and water or AL.

 

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#43 DAVIDG

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Posted 21 October 2019 - 03:20 PM

 As chemist/engineer , let me try too explain  how these  chemical over coatings work to protect silver. They are not  hard physical barrier like what  you get when SiO is vacuum deposited over Al.  What these silver over coatings are trying to do is reduce the reactivity of the silver to oxygen and water. These  coatings do not stop the silver from being reactive with other materials like acids or bases, so the coating can still be easily removed. 

  What is the new exciting addition to the  silvering process is the use of nano-layer protective coating which is discussed in the write up about the process. It is that new technology that makes the silver coating last much longer then other methods used in the past. The chemistry of the silvering  process is the same that was known and used for the last 100 years, just packaged in away that it can be sprayed. Companies  like Peacocklabs  http://peacocklabs.com/products.htm have been offering spray on silver coating solutions since the mid 70's. So the materials offered by Angel Gliding are nothing new chemically just packaged for ATM and other hobbies for small  size jobs.

 

                    - Dave  


Edited by DAVIDG, 21 October 2019 - 03:24 PM.

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#44 SteveInNZ

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Posted 21 October 2019 - 03:21 PM

Hello:

   

  As someone who does live on the Big Island with a (recently) very active volcano, I'm been reading this thread with some interest.  One thing that hasn't been mentioned much is the effect of condensation on the mirror.  For example, I live in warm tropical Hilo, but our observing site is up above 9000 ft. to get above the clouds.  The telescope gets nice and cold while we're observing, and dews over on the drive down.  This is inevitable unless you put your whole telescope into an airtight bag on the way down.  Due to the change in air pressure, warm moist air will make its way into the telescope and condense on everything.  A friend of mine had his mirror recoated at Gemini with their protected silver coating.  After one damp night, the coating was ruined.  

Cheers

Mike

 

I'm just giving this a bit of a bump as I have the same concern. Dew.

Given the choice of the silver with this protection versus a straight (no added overcoat) aluminium in an environment prone to dew, is there a clear advantage of one over the other ?

 

Steve.



#45 Steve Dodds

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Posted 21 October 2019 - 03:50 PM

Just cost


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#46 dave brock

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Posted 21 October 2019 - 05:20 PM

And the fact that the bare aluminium can still be carefully cleaned.

#47 dave brock

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Posted 21 October 2019 - 05:24 PM

Also, in New Zealand, by the time you pay to import the materials and the fact they have a limited shelf life, I'm not convinced there's much if any saving on cost either.

#48 Bob4BVM

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Posted 21 October 2019 - 06:18 PM

Just cost

Far more than just cost for me !

As I stated in post 7 above, for me it's shipping, reflectivity, convenience & cost.

The first one alone is plenty of justification for me.  The very thought of shipping a matched pair of 17.5" binoscope mirrors gives me the willies. I have WAY too much experience with truckers handling of heavy "fragile" parcels to play those odds with my mirrors if I can avoid it.

 

So now, for not a lot more trouble than a good mirror washing, I can have a fresh reflective coating.

By the time I figure in the work of boxing up my primaries for shipping and the time lost in transit & at a coater, home silvering becomes a no-brainer for me.

 

CS

Bob



#49 Bob4BVM

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Posted 21 October 2019 - 06:20 PM

I'm just giving this a bit of a bump as I have the same concern. Dew.

Given the choice of the silver with this protection versus a straight (no added overcoat) aluminium in an environment prone to dew, is there a clear advantage of one over the other ?

 

Steve.

 

Build a ventilation system which prevents primary dewing.

CS

Bob



#50 SteveInNZ

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Posted 21 October 2019 - 06:25 PM

It's the cleaning part that I'm curious about. The accelerated life test in the linked article involved dunking the silvered surface into a solution. Does that infer that cleaning might be an option with the overcoat ?

 

If Angel would sell the Anti-tarnish alone and I can clean it, it may be worth investigating. For me, it's not worth doing the whole thing as I can get mirror silvered locally for next to nothing ($35).

 

Steve.




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