Ice,
mine is a homebrew so will differ, perhaps. Best idea if in doubt is to remove the mirror completely, but in my case I simply wash it in the laundary tub, complete with cell (University Optics alloy cell).
I partly fill the tub with cool to luke warm water, and a slurp of dishwashing liquid (less not more). Allow the dust/crap to soak for a while then swill it off and lightly/gently swab the surface with cotton wool.
Tip on an angle to drain/dry, and then get the last drops with the tissue/towel.
Care is required, but more so you don't drop it.
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