Have you found sliver that is heavily tarnished? Don't worry it'll soon vanish in no time. Ok, make sure that it isn't classed as "treasure trove", if it is then don't clean it until it has been disclaimed. Once disclaimed you may then proceed to clean as follows. Select a container big enough to hold the item(s) you wish to clean.
Line the bottom of your container with tinfoil (aluminum foil) shiny side facing upwards. Add all your tarnished silver and sprinkle approx a cup of baking soda (less required for small items), add boiling water to cover the item(s). You will soon notice a smell of sulphur (or rotten eggs), when your silver looks much cleaner empty the water and use a soft clean cloth to buff up your silver. Job done !
Whatever you do, please do not polish up your hammered coin(s) as this will devalue what they are worth uncleaned. Buyers want to see coins in their orignal state "as found" with patina muck and dirt still intact. Rubbing coins will scratch them because of minute grains of sand in the soil.