[astrospotter (Mark)]

I agree that the sponge is not a good thing at all. Grit will stick in the sponge even if you rinse it. You must use something that can hold a lot of water and you can use fresh ones frequently to minimize any risk of grit in the 'wiper'.

Generally I do something similar to Gama's method but use the cotton balls found in a cosmetic department with a big bag fairly cheap. My mirror comes out so I don't have to do the plastic sheet thing but that was a smart way it seemed to catch the water/soap.

I use very small amount of very gentle dishwashing liquid (not much at all) in slightly warm distilled water. Important to use distilled water to avoid tap water grit from your spiggot/pipes.

Don't do this on a hot day or with ANY chance of sun hitting the mirror through a window (later as it is trying) or outside as the sun moves in the sky. Other reason for not a hot day is that soap stage to dry on the mirror and leave residue that you will then have to 'chase'. ALWAYs do in total shade. I have found that a big mirror can easily focus and burt very quickly anything at it's focal length. Fun for when you are a kid but NOT fun generally for eyes or safety. I share assorted stories with others and trust me, NEVER let the sun hit your mirror in transport to a site, in scope setup in the day, or in forgetting to cover it at night OR in cleaning. It's just 'bad' idea. I have a friend who cleaned scope mirror inside, set it to try and sun moved in to the window and he notices smoke cause the mirror focused on a bookcase nearby. No fire as he was there but it COULD have been real nasty situation to explain to the wife.

Rinse first and let soak for a minute then with mirror at a 30 degree grade angle start at top with GENEROUSly soaked cotten balls and do small area with only the weight of the cotten ball (don't push down on those) and rotate the cotten slightly as you push it so if it does pick up any grit it is lifted and not pushed back on the mirror to grind in a scratch.

Disguard the cotten balls you use rather fast so you don't re-apply with small grit from last pass and always use a LOT of the warm water. Work your way down from the higher part of the mirror to the bottom (let gravity help you drain off the grit).

After this use distilled water and rinse the mirror with trickles of the pure water to remove all soap film. Do this rinse at least twice.

Lastly there are MANY people who claim to not clean a mirror till it gets fairly bad because it is greater risk than reward. This is sort of true but if you have a real nice quartz coating on your mirror it is less of an issue than if you are going to be contacting the Al directly. A non-quartz coated mirror I would say to avoid cleaning too often.

This is obvious but be real careful to not have anything at all that might accidentally drop on the mirror (empty pockets if you have shirt pockets) and have short sleeve shirt to avoid cuff rub and so on. For the ladies, keep your hair tied back.