NOTES:
* Where ammonia is recommended make sure it doesn't contain bleach.
* Ultrasonic cleaners ONLY work with water and water based cleaners.
Info from off the web at:
http://www.mycoincollecting.com/collecting/cleaning-coins.html
The first rule of coin cleaning is: If you don't know its value, don't clean it, or if you think it is valuable, don't clean it, or if you know it is valuable, don't clean it. In other words, do not clean your discovered coins; leave them untouched and stored in proper holders. The reason for this is that coin dealers and collectors are interested in purchasing coins in their original condition and natural state of preservation.
For example, never clean coins with commercial jewelry and metal polishes or silver tarnish remover, which will remove the toning that normally collects over time on copper and silver coins. Removing tarnish often harms coins, leaving small spots, scratches, or pockmarks that can significantly diminish their numismatic value by up to 90 percent! Statistically, nearly 20 percent of coins shown to coin dealers are rejected because they were improperly cleaned, polished, or their toning was chemically enhanced.
The second rule of cleaning coins is take your coins to a professional do the cleaning. Professional dealers often offer a coin cleaning service using a method called "dripping" that should not be attempted by an amateur. Always handle your coins by the edges to avoid fingerprints on the surfaces.
The third rule of cleaning is, if your coins are so corroded that the date and details cannot be determined, consult a professional for advice before attempting to clean the coins to avoid or minimize possible damage.
The fourth rule is, if you absolutely, positively must clean your discovered coins, you should clean them with the least harmful method that will give the desired results. Remember that excessively dirty or spotted coins, if not cleaned within a reasonable length of time, can eventually corrode and become damaged beyond repair. After selecting the method you will use, you should experiment on low-value coins before cleaning high-value coins. Do not be tempted to use harsh chemicals, vinegar, sulfuric acid, abrasive pastes, polishing cloths, metal brushes, rock tumblers, rotating tools, or impact devices which can result in smooth, shiny, metal slugs.
The fifth rule is, if you know a coin you are selling has been cleaned, you must disclose that fact to the buyer
UNCIRCULATED COINS
Never clean a Proof or Uncirculated coin as doing so will invariably introduce minute hairline scratches and ruin any mint luster. If there is dust on the surface, use a photographic squeeze-bulb air blower to remove it.
GOLD COINS
Gold coins, when first struck, are a bright yellow-orange color. Over a long period of time, copper and other trace elements alloyed with gold cause it to tone to a deep orange color, possibly with light brown or orange-brown streaks. Light toning does not affect the value of a gold coin.
Being of a "noble metal" that doesn't itself react chemically with its environment, gold coins are not likely to discolor during cleaning although a centuries-old tone could be removed. Wash carefully in clean, warm, soapy, distilled water with a fluffy cotton washcloth or very soft toothbrush. Because gold is softer than silver, be careful even when using a soft toothbrush for cleaning, as any grit present it will make minute scratches on the surface.
CLEANING SILVER COINS
Silver coins, when newly minted, have a bright silvery-white surface. A chemically active metal, silver tends to tone deep brown to black. Circulated silver coins will often have a dull gray appearance, sometimes with a deep gray or black area. Silver coins acquire a blue, green, or violet oil-like tone through tarnishing that can enhance the appearance and desirability of an old silver coin and should not be cleaned.
Many collectors will not buy silver coins that look as if they have been cleaned. When tarnish becomes dark brown or black, and a coin's design is hard to see, there may be some desirability to cleaning it using non-harsh methods, but never with an abrasive paste or cloth.
Clean dark silver coins with ammonia, vinegar, rubbing alcohol, lemon juice or polish remover with aceton. Allow coins to soak in a container of the liquid until any dirt or encrustation has been dislodged.
Air-dry or pat them dry with a soft, clean cloth. Do not rub or polish. This may scratch the surface of the coin and will remove metal from the coin's surface. Any wear or scratches will decrease the value of your coin!
Note that silver coins can oxidize rapidly, especially in the presence of sulfur, such as is found in paper products. Some oxidized toning can be desirable but black silver coins are not. Only store your coins in proper containers, such as 2-inch by 2-inch sulfur-free envelopes available at coin dealers.
CLEANING COPPER COINS
Copper is among the most chemically active of all coinage metals. When a copper coin is first struck it has a brilliant pale orange surface and turns brown when circulated.
Copper coins tend to look worse after being cleaned and are more easily ruined than gold or silver coins. When absolutely necessary, clean dirty, green crusted, badly corroded copper coins without scrubbing them. Try soaking them in grape oil (or olive oil if grape oil is not available).
Some results can be obtained in one to four days, but don't be afraid to wait several weeks, months, or even a year for desired results. Remember, some of the green patina may be desirable in a copper coin. Although not so much a problem in Colorado, the prudent collector in a humid climate does not collect red copper coins which oxidize badly. Even in Colorado, it is wise to keep a desiccant in proximity to brown copper coins to absorb air moisture. Every six months, check your copper coins and stroke them with a soft camel's hair brush, such as is used on photographic lenses.
Another way to clean copper coins, use a product (available from any good coin supplier) called MS70. Use rubber gloves, this stuff will dry out your skin. It is safe, but if whatever is on the coin is stubborn, the coin can be soaked for days and even weeks in the MS70. You may use a soft toothbrush that will not harm the coins surfaces to remove the dirt in the devices and continue soaking. When you are satisfied with the coin's appearance, neutralize the MS70 from the coin with baking soda and warm running water. Dry the coin thoroughly and then apply a coat of Blue Ribbon coin cleaner and preservative, and let it dry for several days (or as long as it takes). Wipe any excess off with soft cotton balls, and store in safe cardboard 2 x 2's with the clear centers (use the ones that staple shut, not the self stick, that glue dries out and may not be safe). Make sure that the supplier tells you that the 2 x 2's you bought from him are safe. If the coin is somewhat discolored, you can use Dellar's Darkener after the soaking in MS70. Wipe any excess off and let it dry for days, or as long as it takes so that no more can be removed from the coin with a cotton ball. Use this before the Blue Ribbon until the coin is satisfactory to you. The Blue Ribbon is a cleaner also, and may remove some of the darkener, but the end result will be a beautifully clean and conserved coin for your collection.
NICKEL COINS
Nickel coins, when first minted, are dull silver in appearance, not as bright as silver. Circulated nickel coins have a gray appearance. Nickel coins are best cleaned with clean, warm, soapy, distilled water and a soft toothbrush. For stubbornly stained nickel coins, ammonia, diluted 3 to 1 with distilled water, has been used successfully.
STEEL COINS
Steel cents actually rust in the presence of humidity. Although difficult to store properly, "steelies" were made in such large quantities that they are never likely to become rare.
If you have decided to clean your coins, clean them the same day they are discovered to prevent corrosion from continuing to build.
A first cleaning step for any coin may be to soak it for a few minutes and wash it in clean, warm, soapy, distilled water in a plastic container, using a mild liquid dishwashing soap and a very soft toothbrush. This may be all that is necessary. To make your soapy solution, use one tablespoon dishwashing liquid soap to a pint of water in your plastic container. Remember that metal containers can cause galvanic action of dissimilar metal alloys and will damage your coins!
Accumulated dirt and grime can usually be safely removed from a coin with the application of petroleum jelly (such as Vaseline) to both sides using a cotton-tipped swab (such as a Q-tip). Carefully remove the residue with clean swabs and finish with a soft, lint-free cloth.
Isopropyl or denatured alcohol is another non-abrasive cleaner that can be used in place of grape or olive oil. Never, however, use baking soda for a cleaning rub; baking soda may make a coin shinier, but will almost always ruin the coin's numismatic value.
A good example of corrosion that should be removed is Polyvinylchloride (PVC), a chemical found in older plastic coin holders that over time leaves a green, adherent, acidic, sticky, slightly scummy, scuzz discoloration on coins. This scuzz can spread so it is best to remove it as soon as possible using an organic solvent. One such organic solvent is acetone. You must adhere strictly to the warnings shown on the container, as a solvent such as acetone (found in nail polish remover) can be dangerous. Organic solvents can be used to remove tape or adhesive residue.
Some archeologists, professional coin dealers, and metal detecting hobbyists have used ultrasonic tanks that use ultrasound waves to agitate the clean, warm, soapy, distilled water in which coins are immersed. Sound waves are more gentle than even a soft toothbrush.
Expensive, specially made, commercial coin cleaning agents are available at coin shops. These cleaners should only be used as a last resort. You should never put gold coins into jewelry cleaner. Neither should you should dip silver coins in silver dip or polish them.
After cleaning any coin, rinse it with distilled water, not tap water, which contains minerals that may leave spots on the coin. Some people suggest adding a final rinsing in isopropyl or denatured alcohol.
Dab or pat rinsed coins partially dry with a soft, lint-free cloth, then allow them to air-dry without touching each other on a soft cloth without rubbing, which can cause minute scratches.
