To make your mirrors this clean first do not try and dust them with a soft brush of any sort. If you only have dust on the mirror skip to the cleaning step using the soap and cotton balls. Trying to dust a surface first mirror will only scratch the soft coatings and shorten the life span of the coatings.

The most common problem with amateur astronomers optics is the over cleaning of them. I over clean my optics, once a year I "dust" them and once a year I "wash" them. It is recommended not to wash your mirror more then once a year. Every time that you wash your mirror you remove some of the coatings, and degrade the performance.

Once the mirror gets grime and real dirt (not dust) on it, it is time to wash. This is a process works well, is easy, and seems to be safe. Below are step by step instructions with photos to aid you. I can not take responsibility for those who might damage there mirror by following these instructions, continue at your own risk.This is just a process that has worked for me many times.

Ok these are the items you will need for cleaning the mirror.

Notice that the isopropyl alcohol is 99%. I only use this type even though ethyl or isopropyl above 90% should work.

Use only sterile cotton. Regular cotton balls have impurities that may scratch the surface.

Use only distilled water. Purified or spring water still has minerals in it that will cause water spots.

Dishwashing detergent rounds out the items you will need.

Now take the mirror and put it in a plastic colander or something similar. Make sure it is plastic so it will not chip the mirror. The colander allows the water to drain off. Now put the colander with the mirror in the sink and let luke warm tap water run over the mirror.

DO NOT turn the water off. Keep the mirror wet at all times. Do this for at least five minutes. By running the water over the mirror this long any pieces of dirt that could damage the coating will be rinsed away.

If you see dirt on the mirror continue to run water over it until it rinses away. If you are only dusting the mirror skip down to the step where you rinse it with distilled water and continue from there.

Now it is time to wash the mirror. Fill a bowl with water, and add one drop of dishwashing detergent to it.

Take a cotton ball and dip it into the water detergent mix. Using only the weight of the cotton. APPLY NO PRESURE. Start at the center of the mirror and clean the mirror surface using small circular motions.

Keep the water running while doing this. Change the cotton ball often. This will insure that if the cotton ball gets pieces of debris on it, your mirror will not get scratched. Continue until you have washed the whole mirror. Now once again rinse the mirror for at least 5 minutes.

Turn the water off and rinse the mirror with the distilled water. Use the whole gallon of water, this step will rinse away any of the water from the tap removing any chance of minerals in it causing water spots.

After you have rinsed the mirror with distilled water, rinse the mirror with the alcohol. The alcohol will absorb all the water and rinse it away, insuring that you don't end up with spots on the mirror.

This is the reason for using 90% or higher alcohol. The higher the percentage the less water to blot off in the next step. Using 99% I end up blotting only the lower edge of the mirror, the rest of it evaporates quickly leaving to spots.

After the alcohol starts to evaporate gently blot off any excess water that is standing on the mirror with a cotton ball.

Blot do not rub. Rubbing will once again damage your coatings. Blot the excess water off only when needed to stop spotting almost all the alcohol will evaporate off.

When you blot the water off the mirror it will leave little pieces of cotton on the surface. Ignore these. The small amount of cotton on the surface will not noticeably degrade the performance of the mirror.

Now you are done! Your optics are nice and clean. I include this last step to show you what will happen even attaching the mirror to the mirror cell.

Dust will gather (the scratch on the mirror did not happen during cleaning, but during storage of the scope) on the telescope. Try hard not to let anything fall in the telescope tube. Resist the temptation to blow or wipe this dust off. Your mirror will always have small particles on it. This cannot be avoided in a open tube telescope.

Now get that scope back together and start using it.