+CoinsAndPins Posted August 21, 2006 Share Posted August 21, 2006 Someone requested I add a post about how to clean coins. The below information is a guideline based on my personal experience with many years of numismatic coin collecting, several years of logo (exonumia) coin making, and a few years of metal working experience. It is also based on other long term coin collector's and metal worker's experiences that I have learned from. If you have any other recommendations, then please feel free to post. Cleaning a coin and removing minor corrosion Coins plated in polished real silver, real copper, and brass (and also fake silver and gold) will tarnish/corrode over time, even if they are in air tight capsules. Oxidation and intergranular corrosion starts once these metals are exposed to the air, moisture, and/or touched by the acid in the oils on human skin, even during manufacturing. The coins are exposed to the air and humidity long before they are placed in capsules, and factory workers frequently handle them before packaging. The capsules will slow the corrosion process, but will not prevent it in most instances. The best way, but sometimes most expensive way, to prevent corrosion is to have these finishes coated with epoxy at the factory. If you find corrosion on your coin, do not use an abrasive cleaner like tooth paste or compound cleaner. The small amount of abrasive ingredient will start to wear down the finish and can cause a satin look on polished finishes. A regular metal polishing cleaner usually works best, including on most brass coins; we use MAAS brand metal paste cleaner. A polishing cleaner is much safer to use and it removes the light layer of corrosion faster. It also works great on diamond cuttings. Clean the coin immediately when corrosion appears. Letting the corrosion sit too long will cause pitting or etching on the metal. Once corrosion is in the pits, removing it is almost impossible. Over-polishing/cleaning a coin will wear down the finish. Keep the coins clean, but treat corrosion only when it starts to appear. Don't attempt to polish antique finishes. Most antique coins have a thin coat of clear jeweler's enamel applied to them that help with the finish's durability. Trying to polish these finishes will ruin the protective coating and cause the coin to look worse than when you started. There are companies that make zinc, aluminum, pewter, and antique brass coins with no protective enamel coatings or platings. These coins will corrode over time and there is very little anyone can do to prevent it. If you notice corrosion on these coins, you may be able to very lightly and carefully scrape some of it off with an awl or pick, but chances are the coin will just have to suffer with this corrosion damage since scraping can cause surface damage. Be careful when cleaning two-tone finishes such as a coin that is polished gold and the text on the coin is plated in polished nickel. Two-tone finishes are comprised of a regular plating (or base metal depending on the manufacturer) and then have another thin coat of a different finish applied by hand over the first finish. This second coat of finish can easily wear off. It will require a soft touch to polish these finishes. Real gold and nickel finishes are the most durable and longest lasting. They are the finishes we recommend for geocoins. These finishes will require very little cleaning and maintenance. The nickel will eventually corrode if left in high humidity or damp areas, but it will clean up nicely if treated early enough. Solid gold and silver coins These coins should be handled with care. They usually don't need maintenance, but some do over time. These types of coins are typically minted in "clean rooms" to prevent any kind of dust, humidity, and human excretions from getting on them during manufacturing. Real solid gold coins should not need corrosion or tarnish removal since pure gold does not corrode. However, gold that has been mixed with a significant amount of "reducers" could show tarnishing. It is not very often you see this, but there are some out there. Solid silver coins just need a silver cleaner or a metal polish cream like the one stated above. You should always handle these kinds of coins with clean cotton gloves to prevent your finger soils from getting on them. Also, only use high grade, soft, cotton, lint free cloth to clean them. Any kind of cleaning will cause some form of scratches on the surface, so the less handling and cleaning you do, then the better. There are some silver coins made with an added mixture of substances which prevent tarnishing. So if you see one of your silver coins never tarnish, then don’t think it is necessarily fake, it could be .995 silver with those substances added. These same guidelines apply for the plated (some times referred to as "clad") proof-like gold and silver coins. It is best to just keep these kinds of coins in their plastic capsules and enjoy their natural state. Quote Link to comment
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