Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Silver coating life span and protecting methods?

Astrometry ATM Reflector Mirror Making Optics Beginner DIY Dob
  • Please log in to reply
36 replies to this topic

#1 Celestial825

Celestial825

    Sputnik

  • -----
  • topic starter
  • Posts: 37
  • Joined: 19 Sep 2021

Posted 19 September 2021 - 06:37 AM

Hi.
I have recently completed my 6" mirror and need to coat it. Unfortunately I don't have access to coaters and even to spray silvering facilities. Then my choice is limited to conventional silvering methods like Lundin. Then my questions are:
1) Does a conventional silver coating last as long as a spray silver coating? (i.e. up to one year?)
2) how much the "using humidity absorbers inside the optical tube with tight caps" can be efficient in prolonging the life span of the coating?
Thanks for all hints and tips. 🙏🙏

#2 MitchAlsup

MitchAlsup

    Fly Me to the Moon

  • -----
  • Posts: 5,855
  • Joined: 31 Aug 2009

Posted 19 September 2021 - 12:33 PM

It is oxygen that tarnishes silver, not water--although water can provide copious amounts of oxygen to the tarnishing process. The best storage of a silver coated scope is a nitrogen atmosphere.

 

There are coatings, which when properly applied, that can significantly delay the tarnishing of silver. These coatings are applied in a vacuum chamber. Probably something you do not have lying around.


  • Celestial825 likes this

#3 davidc135

davidc135

    Surveyor 1

  • -----
  • Posts: 1,795
  • Joined: 28 May 2014
  • Loc: Wales, UK

Posted 19 September 2021 - 12:37 PM

Is Hydrogen Sulphide not the culprit?  David


  • Augustus and Celestial825 like this

#4 Celestial825

Celestial825

    Sputnik

  • -----
  • topic starter
  • Posts: 37
  • Joined: 19 Sep 2021

Posted 19 September 2021 - 01:26 PM

That's right. But what is Nitrogen atmosphere? (Nitrogen sealed in the optical tube?)

#5 EJN

EJN

    Fly Me to the Moon

  • *****
  • Posts: 5,034
  • Joined: 01 Nov 2005
  • Loc: Between eigenstates

Posted 19 September 2021 - 01:56 PM

In days of old (when men were bold?) it was a common practice to have a hatch on the tube by the mirror, and make a tight fitting cover for the mirror lined with blotting paper. Covering the mirror like this would extend the life of the silver coating.

 

Also in ATM Book I there is a section on applying a very thin lacquer coating to silvered mirrors.

 

post-12877-0-92886200-1534465634.jpg

 

post-12877-0-21058900-1534465716.jpg


Edited by EJN, 19 September 2021 - 01:59 PM.

  • Celestial825 likes this

#6 Bob4BVM

Bob4BVM

    Mercury-Atlas

  • *****
  • Posts: 2,960
  • Joined: 23 Mar 2015
  • Loc: W. Oregon

Posted 19 September 2021 - 04:22 PM

Old processes still work, lest we forget in this "smart age".

THE  SA  ATM books cover it, i see EJN beat me to it, above.

 

Also, check out the work done by the OSW group, using Midas anti tarnish.  They have great online documentation.  Soon enough i hope to be silvering all six mirrors on my new scope.

CS

Bob


Edited by Bob4BVM, 19 September 2021 - 04:23 PM.

  • Augustus and Celestial825 like this

#7 dave brock

dave brock

    Vanguard

  • -----
  • Posts: 2,424
  • Joined: 06 Jun 2008
  • Loc: Hamilton, New Zealand

Posted 19 September 2021 - 07:20 PM

Unfortunately I don't have access to coaters and even to spray silvering facilities.


Where are you located. I've sent mirrors overseas in the past to get overcoated aluminium coatings. A 6" mirror is easily shipped.
  • Augustus and Celestial825 like this

#8 Celestial825

Celestial825

    Sputnik

  • -----
  • topic starter
  • Posts: 37
  • Joined: 19 Sep 2021

Posted 20 September 2021 - 12:18 AM

 

There are coatings, which when properly applied, that can significantly delay the tarnishing of silver. These coatings are applied in a vacuum chamber. Probably something you do not have lying around.

I was going to make a vacuum chamber and a handy pump with car valves that is certainly not enough for aluminizing. But probably it's not too bad for sio2 protective coating that is not interrupted by oxygen. confused1.gif undecided.gif  



#9 Celestial825

Celestial825

    Sputnik

  • -----
  • topic starter
  • Posts: 37
  • Joined: 19 Sep 2021

Posted 20 September 2021 - 12:26 AM

In days of old (when men were bold?) it was a common practice to have a hatch on the tube by the mirror, and make a tight fitting cover for the mirror lined with blotting paper. Covering the mirror like this would extend the life of the silver coating.

 

Also in ATM Book I there is a section on applying a very thin lacquer coating to silvered mirrors.

Thanks EJN. This is what I definitely should do. But how can put a hatch inside a cylindrical tube that is not much wider than the mirror?



#10 Celestial825

Celestial825

    Sputnik

  • -----
  • topic starter
  • Posts: 37
  • Joined: 19 Sep 2021

Posted 20 September 2021 - 12:38 AM

Old processes still work, lest we forget in this "smart age".

THE  SA  ATM books cover it, i see EJN beat me to it, above.

 

Also, check out the work done by the OSW group, using Midas anti tarnish.  They have great online documentation.  Soon enough i hope to be silvering all six mirrors on my new scope.

CS

Bob

I read the Midas articles on their website and seemingly it really works.waytogo.gif but unlunlucky it isn't available where I live. Then I'm going to try benzotriazole:

 

https://www.jstage.j..._9_411/_article



#11 Bob4BVM

Bob4BVM

    Mercury-Atlas

  • *****
  • Posts: 2,960
  • Joined: 23 Mar 2015
  • Loc: W. Oregon

Posted 20 September 2021 - 01:04 AM

I will be doing alot of experimenting on glass samples when i get my Angel G kit

Will try the Midas stuff, but also definitely the highly thinned lacquer as outlined in the old ATM volumes.

Might try spinning the blank on a turntable as they describe in there somewhere

Worst case for me is none of it works, so i have to re-silver every year or two.  That is SOP for Clements on his 70" from what i hear...


  • Augustus and Celestial825 like this

#12 Celestial825

Celestial825

    Sputnik

  • -----
  • topic starter
  • Posts: 37
  • Joined: 19 Sep 2021

Posted 20 September 2021 - 01:55 AM

I will be doing alot of experimenting on glass samples when i get my Angel G kit

Will try the Midas stuff, but also definitely the highly thinned lacquer as outlined in the old ATM volumes.

Might try spinning the blank on a turntable as they describe in there somewhere

Worst case for me is none of it works, so i have to re-silver every year or two.  That is SOP for Clements on his 70" from what i hear...

I like to try the thin lacquer layer too, but the problem that must be treated is the uniformity and thickness of the layer. maybe using the vapor instead the solution is helpful. confused1.gif



#13 Tom Stock

Tom Stock

    Apollo

  • *****
  • Posts: 1,066
  • Joined: 27 Jun 2010
  • Loc: Saint Augustine, FL

Posted 20 September 2021 - 07:13 AM

Midas will reduce tarnish but will not stop things like dead bugs or wet dust from causing spots of corrosion.
  • Celestial825 likes this

#14 Tom Stock

Tom Stock

    Apollo

  • *****
  • Posts: 1,066
  • Joined: 27 Jun 2010
  • Loc: Saint Augustine, FL

Posted 20 September 2021 - 07:18 AM

The old silvering process and spray silvering are really the same process. The difference is just in how the reaction is controlled and the speed of the reaction.

I silvered some beakers for tests and the silvering process itself is not very difficult. I used powerade as a reducing sugar. You must be careful to combine chemicals slowly and discard contents immediately to prevent explosive compounds from forming.

 

I believe the spray silvering method to be superior though for convenience, safety, and the chance of success.  The old method is very sensitive to temperature and timing.

 


Edited by Tom Stock, 20 September 2021 - 07:23 AM.

  • Bob4BVM and Celestial825 like this

#15 Celestial825

Celestial825

    Sputnik

  • -----
  • topic starter
  • Posts: 37
  • Joined: 19 Sep 2021

Posted 20 September 2021 - 09:42 AM

Midas will reduce tarnish but will not stop things like dead bugs or wet dust from causing spots of corrosion.

Thank you Tom. But when the spots appear? (One month, year, ...??)



#16 MitchAlsup

MitchAlsup

    Fly Me to the Moon

  • -----
  • Posts: 5,855
  • Joined: 31 Aug 2009

Posted 20 September 2021 - 11:11 AM

aammo

I did not write what got attributed to me.



#17 Celestial825

Celestial825

    Sputnik

  • -----
  • topic starter
  • Posts: 37
  • Joined: 19 Sep 2021

Posted 20 September 2021 - 12:01 PM

I did not write what got attributed to me.

I'm sorry. This was an undelibrate reply.



#18 DAVIDG

DAVIDG

    Voyager 1

  • *****
  • Posts: 10,481
  • Joined: 02 Dec 2004
  • Loc: Hockessin, De

Posted 20 September 2021 - 12:21 PM

 As chemist the spray method is using the same chemical process as the "old school" method just  repackaged in a pre mixed  containers and applied via spraying. What is the big improvement in the nanocoating applied over the silver to reduce the tarnishing. 

     Another method to reduce the tarnishing is that 3M sells a treated paper that absorbs material that cause tarnishing. I used it with a small mirror I silver coated and lined the cover with one. The coating  was bright  for 3 years until I accidentally forgot to close the cover. 

 

  https://www.amazon.c...32158252&sr=8-6

 

                         - Dave 


Edited by DAVIDG, 20 September 2021 - 03:01 PM.

  • Mike Spooner and Bob4BVM like this

#19 Celestial825

Celestial825

    Sputnik

  • -----
  • topic starter
  • Posts: 37
  • Joined: 19 Sep 2021

Posted 20 September 2021 - 12:47 PM

What is the big improvement in the nanocoating applied over the silver to reduce the tarnishing.

Do you mean that spray silverings contain an anti-tarnish substance? confused1.gif

And thank you for sharing your experience about anti-tarnish strips. 🙏


Edited by Celestial825, 20 September 2021 - 12:53 PM.


#20 Tom Stock

Tom Stock

    Apollo

  • *****
  • Posts: 1,066
  • Joined: 27 Jun 2010
  • Loc: Saint Augustine, FL

Posted 20 September 2021 - 02:32 PM

Thank you Tom. But when the spots appear? (One month, year, ...??)

My understanding is that the coating may last 6 months to a year, but the spots can form quickly depending on how much contamination it is comes into contact with.  I haven't actually silvered a telescope mirror yet so i can't speak from experience.

 

I did silver a beaker, and left it in my bathroom exposed to hot shower air for a month and noticed no visible difference in that time.


  • Celestial825 likes this

#21 Bob4BVM

Bob4BVM

    Mercury-Atlas

  • *****
  • Posts: 2,960
  • Joined: 23 Mar 2015
  • Loc: W. Oregon

Posted 20 September 2021 - 02:33 PM

Midas will reduce tarnish but will not stop things like dead bugs or wet dust from causing spots of corrosion.

Correct Tom, Midas or lacquer will slow the tarnish but is not for physical protection of the coating.

 

You do not allow bugs, dew, or dust to get on the coating... that is what Ed's HEPA air system is designed to prevent. Silver requires special treatment to keep it clean since it is basically not washable like overcoated aluminum.  Important to understand that if one is going with silver.


  • Celestial825 likes this

#22 Bob4BVM

Bob4BVM

    Mercury-Atlas

  • *****
  • Posts: 2,960
  • Joined: 23 Mar 2015
  • Loc: W. Oregon

Posted 20 September 2021 - 02:35 PM

Do you mean that spray silverings contain an anti-tarnish substance? confused1.gif

 

No. Midas or lacquer is a separate step, after silvering


  • Celestial825 likes this

#23 Bob4BVM

Bob4BVM

    Mercury-Atlas

  • *****
  • Posts: 2,960
  • Joined: 23 Mar 2015
  • Loc: W. Oregon

Posted 20 September 2021 - 02:38 PM

I like to try the thin lacquer layer too, but the problem that must be treated is the uniformity and thickness of the layer. maybe using the vapor instead the solution is helpful. confused1.gif

You need to read about the process in the old S.A.  ATM books.  It was std practice then, no need to reinvent the wheel


  • Celestial825 likes this

#24 Tom Stock

Tom Stock

    Apollo

  • *****
  • Posts: 1,066
  • Joined: 27 Jun 2010
  • Loc: Saint Augustine, FL

Posted 20 September 2021 - 02:54 PM

 As chemist the spray method is using the same chemical process as the "old school" method just  repackaged in a per mixed  containers and applied via spraying. What is the big improvement in the nanocoating applied over the silver to reduce the tarnishing. 

     Another method to reduce the tarnishing is that 3M sells a treated paper that absorbs material that cause tarnishing. I used it with a small mirror I silver coated and lined the cover with one. The coating  was bright  for 3 years until I accidentally forgot to close the cover. 

 

  https://www.amazon.c...32158252&sr=8-6

 

                         - Dave 

Hi Dave, there is one difference. The spray on formula uses formaldehyde in the reducing solution.  You probably expected that.

 

The old procedure uses sugar, and if the reaction goes on for too long, on the coating is deposited a brown sludge which I think might be the carbon from the sugar.  I'm no chemist but I am interested in basic chemistry so I was more interested in doing this myself rather than buying the 2 part kit.

 

I tried to do my own 2 part spay method using the old silvering formulas (there are many, but all similar) unsuccessfully, but I did not try using formaldehyde.  The slower method of building a dam around the mirror worked fine (I used a beaker) but the timing is important.

 

Formaldehyde must be the trick to making the 2 part spray work since detecting aldehydes is what the Tollen's reagent is used for to begin with, and I suppose you would end up with less byproducts after the reaction.  

 

I used a sensitizing solution required (Stannous Chloride) before coating. 

 

3 years?? That's impressive.  I'm going to give this another try soon.  The biggest issue for me was fear of damaging (scratching) the mirror during the scrubbing with calcium carbonate.  I was really paranoid that any bit of dust or grit, even in the water itself, might land on my mirror during the scrubbing process and scratch it all to heck.  It was very disturbing scrubbing so hard until the glass squeaks.


Edited by Tom Stock, 20 September 2021 - 03:07 PM.

  • Celestial825 likes this

#25 Oregon-raybender

Oregon-raybender

    Optical Research Engineer

  • *****
  • Vendors
  • Posts: 1,147
  • Joined: 13 May 2010
  • Loc: Oregon, South Western Coast

Posted 20 September 2021 - 03:00 PM

I have sprayed silver hundreds of mirrors (4" to >36") over my years at Tinsley and other companies. I have given to the the Oregon group helpful insights and tech help with their process. They have reviewed the latest process and has developed an improved method both in using the Angel product and the protection of the silver. They detailed the process and have answered many of the concerns listed here. There is no hard overcoat (like used on AL) for sprayed silver. The overcoat is just to allow the coating to last a few months longer. In most cases I have suggested to silver the mirror before the observing time period ( Spring ) and recoat again in 8 to 10 months. The silver coating is what we call a soft coating, with limited methods of cleaning (no touch) and keeping the mirror away from moisture, bugs and dust by covering. I have test mirror in my office which was coated by one of the Oregon member with the Midas and bare coating (50/50). This was over 2 years ago, it looks fine, some edge browning which is normal, stored in Zipper plastic bag, wrapped in lens tissue and paper towel. I would suggest review, read they efforts it would answer many of your questions and concerns. Just be aware, the spray silver is short term soft coating and most likely never be a total replacement of AL with overcoat, they different processes. I understand the why going in this direction because of costs, and shipping issues. I have used the chalk method on the mirrors and never had any issues (on high precision optics). The Oregon group found that cleaning with chalk and distilled water improved and solved the issues they were having with the coatings. Cleaning the glass is the most important issue with spray silvering, edge cleaning is key. Get your chalk from a good supplier.

 

Starry Nightswaytogo.gif


Edited by Oregon-raybender, 20 September 2021 - 10:15 PM.

  • brave_ulysses, Tom Stock, Mike Spooner and 2 others like this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics





Also tagged with one or more of these keywords: Astrometry, ATM, Reflector, Mirror Making, Optics, Beginner, DIY, Dob



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics