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OT: removing anti-glare coating on optics

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  • OT: removing anti-glare coating on optics

    To all those optical gurus,

    What's the best method of removing anti-glare coating on polycarbonate optical lens? The kind that give lens purple hue.

    Some of it has already started to peel (must have been poor manufacturing) and I just want to get rid of it but without affecting the base polycarbonate lens.

    I thought I seek some advice before I start using different acid, solvent, etc.


  • #2
    Pretty much anything that will attack the coating will go for the PC first. The coating is usually something like MgF2.


    • #3
      A quick check confirms what I recalled. Polycarbonate is resistant to a variety of acids including up to 35% nitric acid with no etching even after one month. Magnesium fluoride dissolves slowly in nitric acid. Polycarbonate will even withstand hot (50C) 70% nitric acid for 24 hours.

      Nitric acid is about the only choice as MgF is resistant to just about everything else including HF acid.

      All the usual warnings about acids apply except that with nitric acid you should really pay attention because it will bite you.
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      • #4
        This product, Armour Etch, came up on another site I read. If it works, it may be moderately safer than using straight acid. However, while it apparently worked for the guy who reviewed it, it's reportedly hydrofluoric acid which, as Evan indicated, may not do what you need.


        • #5
          Armour Etch is just a somewhat safer fluoride etch. I wouldn't think it will do much. Check with your optician. Glasses can be stripped and recoated. I've had it done before. They send it out to a lab and it takes a week.

          I did strip a pair of glasses once with polishing compound and a dremel with a felt bob. Took 5 minutes with some polishing compound made for plastics that I had around. Got very frustrated because they were scratched and the AR coating was peeling. Worked better than they were. Can't say I didn't introduce some minor change to the prescription, but I could see just fine.


          • #6
            If it's already peeling, you can try stripping it off with tape.
            Tom M.


            • #7
              Magnesium fluoride isn't attacked by hydrofluoric or other acids with the exception of nitric acid. Mgf2 is used as solid material up to six inch or so to make lenses for the best telescopes. It has a very wide transmission spectrum deep into the infrared.

              As for removing by buffing, the experiments I have performed result in unacceptable changes to the figure of the lens. This may not be noticable for eyeglasses because you are only looking through a very small portion of the entire lens at any one time.
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