Outside of an acetone rinse to remove physical contaminants, the absolute only thing you should do with numismatic silver is to LEAVE IT ALONE

! *ANY* type of cleaning (including the eraser and cloth method in the video above) will be visible to someone who knows what to look for. Cleaned coins sell for significantly less so I would just leave your numi coins as they are.
Heck I would leave all your 90%, and generic bullion as they are because you never know what may be collectible in 50 years. At the very least though I would never clean pre-65 90% or numi stuff, but if you want to polish the heck out of your generic rounds and bars than by all means have at it.