If you ask a collector for advice on how to clean their silver coins, their instinctive reaction will be to tell you not to. Virtually any collector will pay much more money for a rare coin if the surface is scratch-free and the oxidation is original. However, there are some techniques to remove most of the dirt without damaging the silver. Usually, non-collector coins have value only for the cost of silver and can be cleaned as much as you want without affecting their value.
Steps
Method 1 of 2: Methods for Gentle Cleaning
Step 1. Handle rare coins carefully
Touch rare or unknown coins as little as possible, holding them only by the edge - not the face - and possibly wearing gloves made of a lint-free cloth. While they may look dirty or damaged to you, a collector may be willing to pay more for them if you keep them in their natural state and avoid damaging them further.
Store them in Mylar bags or ask a coin dealer for advice. PVC sachets could damage them
Step 2. Soak the coins in warm, soapy distilled water
Add a few drops of mild soap (not detergent) to the glass of water. Gently dip them and leave them to soak, turning them after a few hours. This is the only safe method for cleaning silver-plated coins (even if pure silver is more resistant).
- Tap water contains chlorine, which can cause discoloration.
- Oxidation, a thin gray, black or iridescent layer also called "color change", is not the same as dirt. If coins are rare, color change could also be a sought after feature as it can raise their value.
Step 3. Change the water regularly
The next day, if the coins are still dirty, replace the solution with more fresh distilled water with soap. Repeat the operation every day, until they are clean, while still preserving the color change.
Step 4. Gently dry them
Dab them gently with a paper towel or leave them exposed to the air on absorbent paper. Scrubbing them can be very risky, as you may scratch off the color change. Scrubbing them gently with a soft-bristled toothbrush is usually a safe operation: proceed slowly and gently with valuable coins. The goal is to remove loose dirt, not to rub the surface of the coin directly.
Step 5. Wet them and put them in the freezer
If the coins are still dirty, immerse them again in distilled water, then transfer them to a plastic container in the freezer. Freezing, the water will expand, probably detaching some of the underlying dirt. Once frozen, gently remove the dirt: in most cases you will have to repeat the immersion and freezing operation several times.
Step 6. Remove stubborn residues of dirt with long soaking in oil
In the event that the coins are covered with mud or dirt and do not respond positively to the previous treatment, immerse them in mineral or olive oil. Mineral oil should in no case damage the coin, but must subsequently be removed with acetone; olive oil is also a valid option, but there is a remote possibility of causing damage. Each of these methods could take months to remove stubborn dirt: for best results use a plastic holder for the coins, so that both sides are exposed to the oil.
- Cheap, non-virgin olive oil works better than virgin or extra virgin olive oil, as it is more acidic.
- In case the coins have no value as collectibles, you can go straight to aggressive cleaning methods to save time. If the coins are rare or unknown and you don't intend to wait months, take them to a collector for advice.
Step 7. Check the oil every two weeks
Rinse the coins in warm soapy water to remove the oil. If the dirt is not removed together with the latter, leave them to soak longer. In case you are using olive oil, change it when it turns dark green. Once the coins are clean, rinse them in warm, soapy water; if you used mineral oil, scrub it with a cotton swab dipped in acetone.
Step 8. Use an ultrasonic cleaning machine
It is a machine capable of vibrating coins quickly to remove dirt. Small machines for domestic use are suitable for cleaning coins, but will only remove the lightest and most superficial dirt; larger professional machines are more effective, but must be handled with care. For best results, hang a cup on a string so that it is half submerged in the machine tray, without touching the base. Fill the cup with pure distilled water, then run the machine for a few minutes, brush the coin and repeat the process.
You can also operate the machine without the cup, but dirt or objects on the base of the cup will interfere with the vibration and shorten the life of the machine
Method 2 of 2: Aggressive Cleaning Methods
Step 1. Be very careful with valuable coins
Cleaning a rare collector's coin can reduce its value by more than 50% due to the tiny scratches caused by the removal of oxidation. In the event that the gentle methods listed above have not worked, it is preferable to resort to professional cleaning or to accept the imperfections. Feel free to use the methods below on common, non-collectible coins if you prefer them to have a bright appearance.
- Uniform golden, gray or iridescent oxidation (or toning) is desirable and capable of increasing the value of the coin.
- Even if black or blotchy oxidation is not ideal, vigorous cleaning can still lower the value of the coin, so proceed with extreme caution or contact a professional.
Step 2. Collect dirt from the small crevices
After washing with soapy water, black areas may still be present around the letters or detailed images. In this case, wash the coin again and remove the dirt slowly and carefully using a toothpick or bamboo skewer. Be careful not to scratch as the toothpick could scratch away the oxidation.
Using sharp plastic tools will make work slower, but you will be less likely to scratch the coin
Step 3. Rub it with the silver polish
It is a type of cleaner that cleans metal using acids and abrasives, which erode a thin layer of metal. It's an easy way to polish common coins, but it will almost certainly decrease the value of collectible ones:
- Apply a small amount of polish - the amount of a coin - to a soft cloth.
- Fold the cloth in half to transfer the polish to both sides.
- Place the coin between the two halves.
- Lightly rub both sides of the cloth.
- Rub the coin on a clean spot on the cloth.
Step 4. Rub it with a paste of baking soda and water
This inexpensive alternative to silver polish also scrapes coins, causing scratches that are visible with a magnifying glass. Limit the damage by using distilled water and mixing only a pinch of baking soda into it to make a watery paste. Dip the entire coin into the paste, rubbing it between your fingers for a minute, then rinse. Repeat this process 2-3 times if necessary and finally dry it with a cloth.
Step 5. Remove the most stubborn deposits with ammonium
A thick residue on ancient coins is probably cerargyrite (silver chloride): it may be necessary to remove it, especially if it prevents them from being identified. Immerse the coin in 10% ammonium solution in a hermetically sealed container; remove it after a few minutes, rinse it immediately and then brush it with a soft toothbrush. Repeat the operation as many times as necessary.
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Attention:
ammonium liquid and fumes are corrosive. Wear neoprene gloves and work in a ventilated area.
- Some stubborn residues are the result of various chemical reactions, which may require other treatments. Consult a coin dealer first, if the coin is of value.
Step 6. Use very aggressive treatments only as a last resort
The following treatments are particularly risky: without the supervision of an expert they could remove oxidation or scratch the surface of the coin. They are used more often on ancient coins where the most stubborn residues can compromise their identification or significantly lower their value. Relatively modern, industrially produced coins should only be treated this way if they have poor collector value and bad oxidation:
- Soak the coin for one hour in a 50% solution of water and lemon juice.
- Dip the coin in 5ml of lemon juice mixed with 360ml of olive oil. Heat the solution in a water bath in a safe container keeping it below the boiling temperature.
- The "dipping" treatments can give the coin a shiny silver appearance that some collectors appreciate. However, it is a very risky procedure that can cause the appearance of spots: the help of a professional is highly recommended, although it is possible to purchase immersion solutions to use at home.
Advice
- In the event that the coin is coated with enamel or covered with a slimy green substance (a reaction to the PVC of some types of plastic), remove it with pure acetone. Eliminate the slimy layer with a cotton swab dipped in acetone; on the contrary, remove the enamel by immersing the coin in acetone in a container made of a material other than plastic. Work in a ventilated area to protect yourself from fumes and keep the acetone away from fire and heat. If the coin is of value, contact a professional instead.
- Well-preserved proof coins that have not been put into circulation should have a shiny silver surface without oxidation. Do not clean or handle them, as the lack of scratches and damage is what gives them value. Dust them with a blower and do not scrub them.
- Badly corroded coins are usually too damaged to save, even after the corrosion is removed.
Warnings
- Do not try to use metal tools on the coins - they could scratch the finish.
- Be very careful with coins that appear to have non-plated areas, as immersion could cause the underlying bronze to discolour the silver finish. Be patient.
