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Removing lens coatings?

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#1 tag1260

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Posted 22 October 2021 - 01:50 PM

Can you remove lens coatings from a refractor lens? 

 

Thanks



#2 Starman1

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Posted 22 October 2021 - 02:17 PM

Can you remove lens coatings from a refractor lens? 

 

Thanks

Yes, by polishing them off.  It's a job left to lens makers.


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#3 DAVIDG

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Posted 22 October 2021 - 02:56 PM

 Yes you can do it chemically if it is MgF2. It requires a strong acid. The first thing to try is critic acid. A common form is concentrated lemon juice and it needs to be warm to hot The next is oxalic acid and finally sulfuric acid. They work best as a warm to hot solution. If you are not trained and do not have the proper personal protective equipment  and proper area as in the chemical fume hood, DO NOT  try it. 

   You also have to know what type of glass the MgF2 has been applied to. Most Crown type glasses like BK-7 are very acid resistant so the optical surface will not be damaged, but certain flint type glasses have traces of metal oxides and they will be dissolved by the acids and etch the surfaces.

 

                         - Dave 


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#4 tag1260

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Posted 22 October 2021 - 02:58 PM

Do you soak the entire lens or apply it to one surface?  



#5 MitchAlsup

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Posted 22 October 2021 - 03:03 PM

I have removed the front coating (likely MgF2) from 1989 AP APO using nothing more than cleaning fluid (below) and cue-tips. About 1 hour per sq inch using so little pressure you cannot scratch the glass.

 

Cleaning fluid

a) 1 drop laurel sulfate (dish washing detergent) in 1 shot glass of distilled water--mix thoroughly

b) take 1 drop of the shot glass of detergent and distilled water into a shot glass of distilled water--mix thoroughly

c) take shot glass and pour into glass tumbler

d) take shot glass of 90%-99% isopropyl and add to glass tumbler

e) take shot glass of acetone and add to glass tumbler

 

Dip cue-tip and stroke over the glass using zero pressure.


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#6 Steve Dodds

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Posted 22 October 2021 - 03:25 PM

Some, but not all multi coatings can be removed by putting the lens in boiling sulfuric acid!  I'm not going to try that!   Might even crack your lens.



#7 DAVIDG

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Posted 22 October 2021 - 03:26 PM

I have removed the front coating (likely MgF2) from 1989 AP APO using nothing more than cleaning fluid (below) and cue-tips. About 1 hour per sq inch using so little pressure you cannot scratch the glass.

 

Cleaning fluid

a) 1 drop laurel sulfate (dish washing detergent) in 1 shot glass of distilled water--mix thoroughly

b) take 1 drop of the shot glass of detergent and distilled water into a shot glass of distilled water--mix thoroughly

c) take shot glass and pour into glass tumbler

d) take shot glass of 90%-99% isopropyl and add to glass tumbler

e) take shot glass of acetone and add to glass tumbler

 

Dip cue-tip and stroke over the glass using zero pressure.

 As a chemist I can not see how this would work. You have nothing in that mixture that would react with MgF2 or any of the AR materials used for coating.  All your materials listed are organic and modern antireflective coatings applied to lenses are inorganic.  Either the coating wasn't applied correctly so it wasn't  adhered  so you wiped it off or  your solution  added a layer of material  most likely from  laurel sulfate which is common surfactant over the AR coating to make it less visible but the solution did not dissolve it. 

 

               - Dave 


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#8 DAVIDG

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Posted 22 October 2021 - 03:28 PM

Do you soak the entire lens or apply it to one surface?  

 You take the lens apart and only soak the element with the bad coating. 

 

                        - Dave 



#9 MitchAlsup

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Posted 22 October 2021 - 08:18 PM

 As a chemist I can not see how this would work. You have nothing in that mixture that would react with MgF2 or any of the AR materials used for coating.  All your materials listed are organic and modern antireflective coatings applied to lenses are inorganic.  Either the coating wasn't applied correctly so it wasn't  adhered  so you wiped it off or  your solution  added a layer of material  most likely from  laurel sulfate which is common surfactant over the AR coating to make it less visible but the solution did not dissolve it. 

Before I started, the lens had been "cleaned" by something like a dirty rag, and the coating had "numerous" flakes still attached to the surface. So the coating had to go. I was working the edges of the flakes with the cue tip.

 

But you are correct in that there was nothing in the cleaning fluid that actually dissolves anything (other than grease.)

 

(*) numerous is more than a thousand flakes.



#10 ngc7319_20

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Posted 22 October 2021 - 09:23 PM

Can you remove lens coatings from a refractor lens? 

 

I've removed some coatings that already had signs of "flaking off" using only Kodak Lens Cleaner and q-tips.  I worked a small area at a time with some pressure and liberal amounts of cleaner.  Similar to post #5.  But this only works if the coatings are already coming off.   Presumably they were not applied properly in the first place.

 

I've seen other lenses where the coatings were "in place" but severely damaged by fungus, salt water, etc. -- those needed to be polished off by an optician.




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