2 Gallons distilled water
1 Teaspoon mild dish soap (Ivory, Palmolive, Dawn)
1 Quart Acetone (for very dirty mirrors)
1-2 Packages sterile cotton pads or balls
Rubber surgical gloves. (Optional)
1. Completely remove the mirror from the mirror cell and lay on a flat surface and place a block of wood under the mirror to elevate one side.
2. Mix 1 teaspoon soap with 1 gallon distilled water.
3. Pour 3/4 of the soapy mixture across the surface of the mirror, until any loose dirt has been removed.
4. Lay the mirror flat and place about 1 dozen cotton balls on the mirror. Pour the rest of the soapy water on the mirror, until the cotton is well soaked.
5. Gently push the cotton balls around the surface of the mirror using no pressure other than the weight of the cotton balls.
6. If there is any dirt or spots that were not removed, repeat step 4 using cotton pads soaked with acetone instead of soapy water.
7. Once all of the dirt has been removed to your satisfaction, rinse the mirror with 1 gallon of non soapy distilled water and wipe gently with dry cotton pads (using almost no pressure) until the surface is dry and streak free.
When Not To Clean:
When you receive your freshly coated mirror it will look as clean as it ever will. Within hours of being installed in your telescope, the mirror will be covered in dust specs. Especially at night with a flashlight. You will probably want to clean it after just a few days of using it.
Excessive cleaning is the main reason coatings fail. Even the gentlest of cleanings on a first surface mirror will wear microscopic holes in the overcoat, allowing moisture, oxygen and pollutants to get in and start damaging the base aluminum.
Even the filthiest mirror will show NO degradation in optical performance. Just a loss of reflectivity.
Most astronomers clean their mirrors once or twice a year. And keep the mirror stored securely when not in use.
When To Clean:
A mirror should be cleaned when itís so dirty you just canít stand it anymore. Or in the spring, which ever comes first.
You should also clean your mirror if something is spilled on it, especially if it is something acidic, or alkaline. In that case get it off right away. Bottled drinking water can be used in an emergency. Rinse then BLOT with a clean cloth. NEVER NEVER NEVER wipe you mirror.