The cleaning of old coins should be done in a manner that preserves their value. These coins get damaged either if they are rubbed or come in contact with abrasives. Another precaution that needs to be taken is to protect the coins from oil exuded by hands. Using latex gloves serves the purpose. Coins should be handled by their edges in order to protect the engravings from any kind of damage. Methods for Various Types of Coins Before cleaning a corroded coin, advice from a professional should be taken. Always begin with coins that have low value. It minimizes the risk of losing precious coins. Gold Coins In chemical terms, gold is considered a 'noble metal'; which means that the metal doesn't actively participate in chemical reactions. Thus, over time, gold develops just a light tone of orange―yellow color. Being chemically less active, gold is not discolored while cleaning. It is generally cleaned with warm soap water. One should use distilled water for washing the coins. Later, they should be dried carefully. A cotton wash-cloth is generally used for drying. The coin should not be rubbed in any case. This is because, even tiny particles can erode the surface of gold. Silver Coins Unlike the metal gold, silver participates actively in chemical reactions. The tone of silver coins turn deep brown to black as it gets older. Silver coins that are in circulation, appear to be dull gray. The unhanded parts of these coins turn black or deep gray in color. The chemicals used to clean silver coins are vinegar, lemon juice, ammonia or acetone. The coins are soaked in the liquid used for cleaning. The liquid removes any layer or encrustation over the surface of the coin. Coins are dried with a clean and soft cloth. Silver coins should be kept away from chemicals such as sulfur. It prevents the oxidation which leads to blackening. The coins should be preserved in special paper envelopes which prevent the reaction. Copper Coins Copper reacts quickly to chemicals and is the most active metal amongst those used for striking coins. The initial color when it is freshly minted out is pale orange. However, over time, it becomes brownish. Cleaning is done with the help of grape or olive oil. The coins are soaked to clean the corroded or green-crusted coins. It may take a long time to free the coins off the chemical layer. MS70, a synthetic product, can also be used in the cleaning of copper coins. The coins are soaked in this chemical and then washed in warm water. One can use a soft brush after it is soaked. The cycle of soaking and cleaning could be repeated, until the desired result is obtained. Nickel Coins Old nickel coins have a gray appearance. Warm water, toothbrush and soap are needed for cleaning nickel coins. Washing in soap water, followed by cleaning with a soft toothbrush serves the purpose well. To clean the stubborn stains, ammonia could be used. Ammonia should be mixed with distilled water, in a 3:1 proportion. It requires a lot of patience in cleaning these coins and one cannot rush with the process or else, that could ruin the precious coins. If necessary, expert guidance and help should be taken.