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How do I clean corrosion product off prisms?

binoculars
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#1 DrJ1

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Posted 22 May 2020 - 03:04 PM

I bought a legacy 10x50 Selsi binocular that "was in good condition" but obviously had dust on the eyepieces.  Turns out the Left occular arm is completely fractured.  The seller refunded my money and said keep them.  As part of my binocular education, I took them apart and found corrosion product on the prisms, and I suspect the corrosion etched the prism surfaces.  What can I use to remove the corrosion product from the glass without further damaging the surface?  I tried dilute soapy water, camera lens cleaning solution, dilute hydrogen peroxide, and iso propanol but there still appears to be mico surface damage to the prisms.  I taught metallography at the college level ages ago, but I don't have equipment access, or micro-abrasives, to do a quality polish job on the prisms.  It is probably not worth the polishing effort for these old binocs but I may need some of the parts. Can you recommend a cleaner in the unlikely case that the prisms are not etched?  Thanks, DrJ1



#2 hallelujah

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Posted 22 May 2020 - 04:50 PM

https://www.cloudyni...s/#entry9907909

 

Stan



#3 publin

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Posted 23 May 2020 - 06:44 AM

I bought a legacy 10x50 Selsi binocular that "was in good condition" but obviously had dust on the eyepieces.  Turns out the Left occular arm is completely fractured.  The seller refunded my money and said keep them.  As part of my binocular education, I took them apart and found corrosion product on the prisms, and I suspect the corrosion etched the prism surfaces.  What can I use to remove the corrosion product from the glass without further damaging the surface?  I tried dilute soapy water, camera lens cleaning solution, dilute hydrogen peroxide, and iso propanol but there still appears to be mico surface damage to the prisms.  I taught metallography at the college level ages ago, but I don't have equipment access, or micro-abrasives, to do a quality polish job on the prisms.  It is probably not worth the polishing effort for these old binocs but I may need some of the parts. Can you recommend a cleaner in the unlikely case that the prisms are not etched?  Thanks, DrJ1

HI  Drj1!     is  the   corrosion  ? or   tiny  spot   that   can  be  from   aging  kind of  tiny  chips.?[  you  can"t  do nothing  if it is]  some times   the  problem is on the  internal  lenses  but   be   reflected    to    the prism  surface.   anyway if  you take out  the prisms   try   very tiny!    drop   of  wd40  on the  corrosion   spots  and leave it  for  few  minutes   [  I  didn't   try it   realy ]  but  as  I  know   WD40   will   melt   the  corrosion  in   meny   purposes.   any way  you  will   clean  the prisms   after  with   iso propanol or  alcohol  99%   as I  use. hope  it will help you   regards  -  publin



#4 DrJ1

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Posted 23 May 2020 - 08:31 AM

Thanks Stan.  I guess the final word on Ponds cold creme is that it probably doesn't work. DrJ1



#5 DAVIDG

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Posted 23 May 2020 - 09:06 AM

 Having both made and reworked many optical surfaces, the corrosion is most likely a metal oxide. If so a mild acid is needed to dissolve it. If it has etched the glass, the surface will need to be reground, polished back to  an optical polish on  pitch and figured back to optically flat. Since the prism is most likely a common size you might be able to purchase a replacement from Surplus Shed

    As for the eyepiece when you said it fractured, is the glass itself broken or it is just the cement holding the two elements of the lens together. If it is the cement then that is pretty simple fix to separate the two elements and recement them.

   Here is  a link about a pair of binoculars I just restored showing the process and another from awhile back on the different set that also shows how it is done.

 

https://www.cloudyni...elvinator-6x30/

 

https://www.cloudyni...ecement-a-lens/

 

               - Dave 



#6 DrJ1

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Posted 26 May 2020 - 12:02 PM

Dave:  Thanks for the edification and I commend you on your bravery!  When my lab closed, I took several tubes of fine diamond polishing paste out of the trash.  Assuming that I can find them, I might try to polish a prism on a flat plate of glass.  I recall that we used "Linde B" 0.05 micron alumina powder for final polish on metal specimens.  DrJ1



#7 DAVIDG

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Posted 27 May 2020 - 10:11 AM

 I would recommend that you use cerium oxide optical polish and you'll need to polish the prism face against a pitch lap.  The book "Amateur Telescope Making:"  has a couple chapters on making prisms which explains the process. 

 

           - Dave 



#8 Chomatic Aberrant

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Posted 29 May 2020 - 04:13 PM

Hi DrJ.   

 

I started a topic with a similar question some time ago.  Stan provided a link to it above. I initially thought my Rangemaster prisms were the victim of fungus.  After going around and round with remedies suggested by these good folk, none of which worked, it dawned on me that my problem might not fungus. It was some kind of metallic-looking corrosion.  In desperation (and after first trying it on a junk prism) I found that Muriatic Acid did the trick.  Removed whatever it was almost instantaneously, No harm was seen to the polished faces of the prisms nor to the coatings.

 

Good luck.  CA

 

 


Edited by Chomatic Aberrant, 29 May 2020 - 04:15 PM.



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