What is the best way to clean an old telescope mirror?
As a graduate student, I was once asked to clean a 1-meter telescope than had just flown on a high-altitude balloon to do infrared observations. The best method I had devised was to very lightly swab the surface with a cotton swab dipped in denatured alcohol to get rid of the dust. This took me about two hours. For amateur telescopes, it depends on just how bad off they are. If the ‘silver’ has tarnished brown in many areas, the only thing you can really do is to invest the $40 – 50 to have the surface professionally stripped and re-aluminized and over coated. If the surface is in good shape, but just covered with dust, I don’t see, off hand, why a very light cotton swabbing with denatured alcohol wouldn’t be OK. I suggest contacting a local chapter of an amateur astronomer society, however, or calling one of the many telescope manufacturers listed in the popular magazines such as Sky and Telescope, or Astronomy.
