Incorrectly cleaning old or ancient coins can significantly reduce their value leaving them worth only a fraction of their original price.
Never clean valuable coins yourself but take them to an expert coin conservator. In fact never clean coins of any value until you are an expert in correct cleaning techniques. You should leave most coins alone but coins that can be cleaned include the following:
• Coins discovered using a metal detector like many Ancient coins
• Coins that have accumulated a very dark covering of tarnish
• Coins with a localized problem or with tape residue.
• Coins left too long in a vinyl/plastic holder resulting in a thin film on the surface
Cleaning Dirt on Coins
If your coins are dirty and you rub, scrub or polish the coin you will scratch the coin as dirt is an abrasive. When cleaning a dirty coin use a small paintbrush such as the ones used by artists or a soft toothbrush rinsed in warm water to further soften it. Gently exert pressure only targeting the areas covered with dirt. If this does not do the trick and your coin is very crusty and dirty you could try soaking it in olive oil for a day or two and use a toothpick to gently pick off the dirt. You should try not to apply too much pressure in the process. If you work under good lighting and use a microscope or magnifying glass you can clean the coin more precisely and check you are not scratching the coin in the process.
After gently using a paintbrush, toothbrush or toothpick rinse the coin under warm water to remove any loose dirt and repeat the process if necessary. When drying the coin you should not use paper towels as the wood fibres in the paper may leave small hairline scratches. Instead use a cotton cloth, preferably one that is 100% cotton avoiding pressure or rubbing.
Cleaning PVC Film on Coins
PVC damage on coins is caused by plastic holders degrading. Plastic fold-over holders called flips are notorious for causing PVC damage. Other types of coin storage can contain PVC, including cheap Chinese made coin albums, storage sheets, coin boxes etc. Over time PVC can seep out of the vinyl and onto your coins. This can cause an oily film, green spots or a light haze.
If the plastic you store your coins in is soft and if you can smell the plastic then usually long term storage in these holders will result in PVC residue and damage to your coins. Your coins are not damaged beyond repair. In fact it is fairly easy to remove PVC residue on coins but you must do so with care.
Acetone is a chemical used in nail polish removal and works well at removing PVC film and marks from coins. However you should be careful as acetone is very toxic and explosive. Be sure to wear latex gloves and eye protection and to carry out the procedure in a well-ventilated area. Also be sure to read the label.
Pure acetone is best and can be found in your local drugstore in the cosmetics section. You can also find it in hardware stores in the paint section.
Use a clean swab containing pure acetone and gently wipe or dab the swab on the coin until the PVC is removed. Repeat this process using a different swab until the swab is clear.
Cleaning Lacquer Off of Coins
A hundred years ago, some collectors attempted to preserve the quality of their coins by applying a thin coat of lacquer. Nowadays people may lacquer coins if they want to hide scratches or damage to otherwise valuable coins. Therefore be wary of coins covered in lacquer as you may get ripped off. Also be warned that no certification service will grade a coin that has a lacquer remaining on the surfaces Therefore if you want the coin certified you must remove the lacquer first.
Again as with cleaning PVC from a coin you can use acetone to remove lacquer. Dip your coin in acetone for a minute or two. If lacquer remains on the coin you may need to continue the process. Again be careful as acetone is a dangerous chemical.
Removing Tarnish or Toning
Do not worry about removing light toning as a lot of collectors pay higher premiums for well-toned coins. However if you really don’t like the look of tarnish or toning on your coin you can buy chemicals specifically formulated for removing tarnish. You can find these chemical ‘peels’ at your local coin dealer. E-Z-Est Coin Cleaner or jewel luster is great for this purpose. To be on the safe side you should dilute the chemicals used by mixing with water and dip the coin in the solution and leaving it to do its work.
Do not dip coins of different metals in the same solution as it can add another layer of metal. Also do not dip copper coins in this solution as they can react badly. When using the solution dip the coin in and remove straight away. Don’t forget to use a soft cloth towel to dry your Coin, preferably one made of cotton. Dry by patting not rubbing
Heavy toning can hide faint hairline scratches which can reduce the value of your coin so be ready for this disappointment. Also remember that once the tarnish is removed it can leave the coin with an unattractive dull color with no luster.
Remember that when in doubt leave the coin alone as many coins have been irreversibly damaged and have lost their value after cleaning or dipping the coin in chemicals. If you think the coins are worth something and they are really in need of a clean you should leave the job to an expert.