Great report, Don. Looks like a regular "wash" cleaning schedule is best, and contrary to my understanding of washing infrequently and only as needed. I cannot help myself, though, due to the dust in the local area. So, I wash it more than a few times a year. I hear water, however, is not good for the surface or substrate. So, I guess it should be dried soon after a wash.
I rinse it at an angle so the water runs off, then tip it so only a few tiny drops of distilled water are left, then place the mirror on edge on a towel and let dry.
A few drops of distilled water evaporate almost immediately.
It may be harmful to let the mirror soak in water for a long time, but not for a few moments and only a few drops.
The issue is tap water. In my home, as in many places, the tap water contains dissolved minerals and salts. These can easily interact chemically with the aluminum through the tiny
pinholes in the overcoating, so it is not a good idea to let the mirror sit in tap water, even when cleaning.
I've started using distilled water for the soapy bath as well as for the rinse to avoid any problems from the minerals. We all know that tap water can leave spots when it dries.
Distilled water doesn't.
And dew in many city environments is mildly acidic due to the presence of SO2 in the air, and ozone is a hyper oxygenator, so our mirror coatings are doomed in the long run.
At least aluminum oxide sticks to the aluminum, unlike iron oxide to iron.