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Posted by Rick Crockett on April 20, 2007 05:23:45 UTC

Could be either from oily deposit right out from the air, which alcohol or dish soap should be able to remove. It could be from the breakdown and oxidization of the coating. If you hold the mirror up to a bright light, do you see lots of holes, scratches and the bright object? If so then yes it probably should be recoated. Hazy appearances may be due to scattering from dielectric coatings but probably not in relatively inexpensive scopes. The hope is the gain in relectivity and transmission offsets the loss of contrast due to scattering. Dielectic coatings really grab oil films and hold on to them. They are hard to clean and a dry tissue will just push the oil around. Still they are expensive and not used on very many small relfectors.

I remove my own coatings but the solutions can range from nasty to extreme. I use aquaregia with is a molecular combination of two strong acids. Ferric Chloride should work fine but Radio Shack, a common supplier sells a used solution that barely works. It is used to etch copper circuit boards and works well on aluminum without etch the glass. Alway minimize contact with any stripping solution to avoid damaging the optic.

You can silver the mirror and instructions are availible in various books but the best way is to take it to a mirror recoater. I did my 22" and the recoater let me do it myself. Silver coating requires following up by burnishing with a clean soft chamois skin. I would recommend sending it to a commercial coater for a coating and overcoat. -Rick

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