Save desilvering mirror edges?

I have a large wall mirror in our bathroom, secured with the usual clips. In places the bottom has desilvering or blackening about 1.5 inches up from the edge.
I intend to cover the edges with wood framing to hide the bad spots, but it would be good to find a way of "stopping the rot." Does anyone have experience with a product I can safely use to seal the bad parts of the silvering before I cover them?
Thanks, Alexander. (My mail is at shaw.ca and you can call me fony.) Alexander
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The mirror was not properly sealed and it will continue to decay over time. Replacement seems most practical and probably most economical.
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Alexander Miller wrote:

    For what it is worth, I had the same thing happen and used fingernail polish to stop the progress of the de-silvering. I think I had read it was moisture that was the culprit.
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Thanks for the info. Do you think the nail polish has been successful, and how long ago did you apply it?
::    For what it is worth, I had the same thing happen and used fingernail ::polish to stop the progress of the de-silvering. I think I had read it ::was moisture that was the culprit.
Alexander
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Alexander Miller wrote:

    I applied it something like twenty years ago, and there has been no further deterioration of the silvering. Was it luck or the the nail polish? I don't know, but I am betting on the nail polish.
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krylon clear spray lacquer
it's caused by any number of things, but mostly because of something slightly acidic.
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Alexander Miller wrote:

We have the same with large wall mirrors in baths which have bottom edge of mirror sitting on the top of the backsplash behind sink. I'm sure the problem is condensation running down mirror and then wicking in behind the mirror. I would get the mirror as dry as possible and then run some clear silicone caulk along the edges.
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It will not stop unless the bad part is cut off. I would take it to glass shop have them cut off 2 inches, sand the edge and seal the entire mirror. Shouldn't charge you too much. Actually if you get lucky the guy in the shop would do this for a tip, $10 or so. Just have him come out and take a look at it BEFORE going in the office. He might just do you a favor instead of making a ticket on it. If you get it cut don't forget you will have to lower your top clips. (if you were my neighbor, I would do it for free <G>)
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