English milled coins cover c.1663 to the present (plus Oliver Cromwell), including gold coins such as Guineas and Sovereigns, silver including Crowns and Shillings etc, and copper and bronze Pennies, Halfpennies and Farthings.  Condition is the most important aspect relating to a coin’s potential value, also known as grade of preservation.  The grade of a coin can never be improved by cleaning so the best policy is - don't do it!​