Hi toasted; The best way to clean off the grey oxidation is as follows ok:
Take a square piece of tin foil. Use the shiny side toward the coin. Form a small cup to put the coin in.Fold up the sides of the foil. Then pour table salt into the pouch you made. Set the coin in it. Then pour CLEAR Vinegar in the pouch making sure to cover the coin completely. Then pour more salt on top of the coin completely. Fold the foil down over the coin so it actually touches the coin. Wait about 20 - 30 minutes and open it up. You will see the grey is gone except for a few small spots. Use a toothpick to GENTLY push off the remaining dirt. Rinse the coin and pat dry. If there is some small grey left just repeat the steps above. I guarantee you THAT will remove ALL of the grey. Make sure to use fresh tin foil each time ok. DO NOT use the same piece of foil because weirdly the process will reverse itself and put the grey back on and I promise you will "NEVER" get that grey off ever again ok. Slow and steady does it. Good Luck. It works on ALL silver coins without harming the Patina or scratching them ok. Nice Find. PEACE:RONB
PS: Morton Salt works the best ok. Yup, I've tried them all.