How To Clean Silver Coins
Silver coins exposed to the atmosphere for long periods will become tarnished and go black. This is due to the sulphur contained within the atmosphere. It will gradually oxidize the silver.
Silver such as plates, trays, pots and so forth need to be regularly cleaned and in Victorian times this was the duty of servants.
Silver coins however are a different matter. Unless you are an experienced cleaner it is unadvisable to clean any silver coins, especially old ones which are uncleaned. Many collectors prefer the older coins that way as it lends a certain authenticity to the coins.
Probably the only coins one should clean if really required are junk coins or early circulated silver coins. The condition is not critical as one is usually only interested in the silver content but to make them look a bit brighter one can clean them up with a soft toothbrush and some warm distilled water. Don’t use CLR or any cleaning agents on the coins as it will likely remove the silver. Olive oil is also good but you will need to soak the coin for a week or two then you can remove any residual dirt with a soft toothbrush.
At this point if there is still any dirt it is best to leave it.
What ever you do, do not soak silver and any other metal coins in the same water. Sometimes a chemical action can occur resulting in a loss of silver from the silver coin. Bronze is an example of this
Cleaning silver coins is a precarious activity at best and really the best advice if one is in any doubt at all is to simply not clean the coin at all.