I've shared this many times before but it's always worth a look so sharing again.
I have hundreds of sterling charms. Jewelry tarnishes - fact of life. Every so often I decide to clean them all. I take a long knee length man's cotton sock - I always use white - dump a bunch of them into the sock then tie it off. Toss it into the wash with the next load of clothes. That's right - the washing machine - sometimes I do 2 or 3 socks in one load. Just run your laundry like normal. When the loads done put your clothes in the dryer (dah).
Take your sock out and spread the clean charms out on a clean towel. I generally just let mine air dry but if your in a hurry use a hair dryer to dry them out. You can also do this for your favorite charm bracelet or necklace.
I generally do not throw anything in there that has stones in it. Your going to be amazed at how clean your sterling charms will come out. Saves ton's of time and does a much better job than if you took the time to polish each one individually.
If you have invested in the right - solid - American - vintage sterling charms you will be just fine. If you bought some bargain sterling from India or China I would not suggest this method as we have no clue what the heck their actually made of.