Collecting coins is a hobby that has been taken up by people all over the world. Some collect older or historically significant coins for the sole purpose of selling them and making money, while other people tend to hold onto the coins for sentimental reasons. Whatever your reason for buying coins, when it comes to the act of cleaning coins that you may think of as 'dirty' or 'old-looking,' there are a couple of reasons not to do so.
Value of Natural Patina
As coins get older, it is natural for them to develop a sort of film all over their surface called a "patina." Some people think that this patina has to be removed in order for a coin to be considered of any value. This simply isn't the case. The patina on a coin can just as easily be an integral part of the value of a coin. Imagine a coin collector looking at a brand new penny from the mint and a 100-year-old penny. It makes sense for the brand new penny to glisten in the light and have very few, if any scratches. However, it seems out of place for a non-mint, 100-year-old penny to look so shiny. If they were to add it to their collection, it might even look artificial alongside worn, faded, dusty coins that were kept intact by being protected from further damage instead of someone attempting to clean them.
Possible Damage to the Coin
You can cause permanent damage to a coin by attempting to clean it. When a coin is damaged by cleaning, it just means that it will break down and wear out at an accelerated rate. The oil from your fingers touching the coin can cause damage. Any brushes, picks, or scrapers that you may use in order to remove dirt or debris creates scratches and nicks. Any chemicals (toothpaste, vinegar, baking soda, etc.) can encourage corrosion--especially since most natural and human-produced cleaning agents contain acids which are meant to eat away at whatever they come in contact with.
If you have a coin that you think is in dire need of cleaning (for example, polyvinyl chloride damage), take the coin to a professional. This professional may have the methods, equipment, and chemicals to be able to clean your coin as effectively as possible while causing the least amount of damage to the structure and value of the coin. For more information about coins, visit Beaverton Coin & Currency.