Don't Devalue Your Coins By Cleaning and/or Polishing Them
This is a short guide to explain why the numismatic world frowns upon cleaned coins and those that perpetrate the deed. If you are considering the purchase of a coin display gift set for a loved one, then ensure the coins within it are not spoilt by the said process: remember that all that glitters is not gold...
The cleaning or polishing of coins is not recommended. The value of a coin can depreciate by 90% or more if it has been cleaned or polished using chemicals or commercial metal cleaners. There is not a safe way to chemically clean coins without harming them and reducing their value.
Cleaning coins by hand, using a brush of some description, is a fraught business. Even when being very careful a bristle will likely scratch the coin face to some degree.
Silver coins are often more prized by collectors if they have a lightly toned surface and whilst cleaned or polished nickel, copper and bronze coins can look attractive to the untrained eye neither a coin collector or dealer would want to buy them.
The often told story of the wife who decided to clean and polish her husband's coin collection with "Brasso" whilst she was cleaning her ornaments is not apocryphal.