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Thread: Chemical-Stripping a Severely Cloudy 10" 1/6.3 SCT Corrector Plate?

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    Default Re: Chemical-Stripping a Severely Cloudy 10" 1/6.3 SCT Corrector Plate?



    Sir (Bill), I agree with you, I think there's a very high possibility that some form of coating is still remaining on the base glass.

    Reasons:

    1. The extreme edges of the plate, on both sides, is clear. Judging by that, it could be theorized that Meade doesn't coat the extreme edges where the plate comes into contact with the fiber washers (the ones compressed by the retaining ring).

    2. The random "clear spots" that I initially thought were strange, are just places where a previous owner has attempted to mechanically polish (I think). I'd guess that a Dremel tool was used with "felt polishing wheels"...the spots are about that size. That process of removing the coating this way seems to have been successful too...the glass in the center of these areas is crystal clear, and you can actually see where the coating starts and stops on the main glass.

    I used a small penlight to try to estimate *surface quality*, and it actually look quite excellent. I mean I have no idea if the optical figure is f*****, but the surface looks ok.

    ---------

    This morning, I used a Dremel + felt polishing wheel + 3M "Rubbing Compound #39005" to try and follow suit. The rubbing compound came from 3M "Headlight Restoration System", 3M product #39008, from Advance Auto Parts.

    Fortunately, I had the clear area on the edge of the plate to test this process on. I put some of the compound on there, spun the Dremel up to high speed, and pressed HARD into the edge. Then cleaned with 70% Isopropanol, and inspected carefully. Result: No change in the surface was detectable by eye, however, I had intentionally over-run the clear area a bit and the coating had become substantially more clear. It's still screwed, but better.

    So, I ran it across 1/3 of the whole collector plate on both sides. It doesn't seem to be aggressive enough, but that's better than too aggressive, but none of it matters if I can't get it 100% clear.

    I think what I need, is a buffing compound that is aggressive (hard) enough to remove what remains of the coating, but not hard enough to get into the glass and modify the optical figure.

    So basically I just a few grams of Unobtainium (Ubm). That's all.

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    Default Re: Chemical-Stripping a Severely Cloudy 10" 1/6.3 SCT Corrector Plate?

    (Adding an additional post for topic-separation clarity).

    OK so boiling Sulfuric+Boric Acids didn't TOUCH this coating...and I think I need Unobtainium polishing compound to mechanically remove it. I think that I should go back to the chemical stripping process.

    Whatever remains on this base glass, I seriously doubt that it's MgF because that extremely well-written article said that that acid-boiling process would work - and then it did exactly nothing.

    This indicates to me that it's probably just a different layer of the optical coating, and requires a different solvent.

    Can anyone hazard a guess as to what it might be?

    Zoomed-out pic shows the top 1/3 of the plate where I used the aforementioned 3M Rubbing Compound (on one, and both sides, as seen by the difference in clarity).

    Closeup pic shows area where I think the previous owner tried (seemingly successfully) to mechanically polish. Wish I knew what they used.

    Attachment 186658
    Attachment 186659

 

 
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