Clean Silver Coins

When you ask a coin collector for cleaning advice, the gut reaction is usually "don't do it!" Almost all collectors will pay significantly more for a rare coin if its surface is unscratched and the tarnish is left as-is. That said, there are a few ways to remove the worst of the dirt without damaging the silver. Non-collectible coins usually have value only because of the cost of the silver, and you can polish them as much as you like without affecting their price.

Steps

Gentle Cleaning Methods

  1. Handle rare coins carefully. Handle rare or unidentified silver coins as little as possible. Hold them by the edge only, not the face, and ideally wear lint-free cotton gloves. Even if the coin looks dirty or damaged to you, a collector may pay more if you leave it in its natural state and avoid further damage.[1]
    • Store rare coins in Mylar plastic coin flips, or ask a coin dealer for alternatives. PVC coin flips can damage your coins.
  2. Soak the coins in warm distilled water and soap. Add a few drops of mild soap (not detergent) to a glass of warm distilled water.[1] Put the coins in gently and leave them to soak, turning them over every few hours. This is the only guaranteed safe way to clean silver-plated coins (though pure silver is a little hardier).[2]
    • Tap water contains chlorine that can lead to discoloration.[1]
    • Tarnish (a thin layer of grey, black, or iridescence also called "toning") is not the same as dirt.[3] If the coin is rare, toning may even be a desirable feature that raises the coin's value.[1]
  3. Replace the water daily. The next day, if the coins are still grimy, replace the water with fresh distilled water and soap. Repeat daily until the coins are clean (but still have their toning).[2]
  4. Dry carefully. Pat the coins dry with a paper towel, or leave them on an absorbent cloth to air dry. Rubbing the coins is very risky, since it can scratch through the toning.[2] Careful brushing with a soft-bristled toothbrush is usually safe, but work slowly and gently with valuable coins.[4] The goal is to dislodge loose dirt, not to brush the coin's surface directly.
  5. Wet and freeze the coins. If the coins are still dirty, soak them in distilled water again. Transfer the wet coins to a plastic container in the freezer. The water will expand as it freezes, hopefully breaking off some of the dirt from underneath. Gently pat or brush off dirt once frozen. In most cases, you will need to repeat the soaking and freezing several times.[5]
  6. Remove heavy dirt buildup with long-term oil soaks. If the coins are covered in mud or dirt and do not respond to the methods above, soak them in mineral oil or olive oil. Mineral oil should never harm your coin, but must be washed off with acetone afterward. Olive oil will also work, but there is a slight chance of damage.[5] Either one can take months to clean extra-dirty coins. For best results, prop the coins up on a piece of plastic so both sides are exposed to the oil.
    • Cheap, non-virgin olive oil works better than virgin or extra-virgin, since it is more acidic.[6]
    • If the coins are not valuable as collector's items, you can skip to the harsh cleaning methods instead to save time. If the coins are rare or unidentified and you don't want to wait months, take them to a coin collector for advice.
  7. Check on the oil every couple weeks. Rinse the coins in warm, soapy water to remove the oil. If the dirt doesn't come off with it, leave the coins to soak longer. If using olive oil, replace it whenever it turns dark green.[6] Once the coins are clean, rinse them in warm, soapy water. If you used mineral oil, wipe them with a swab dipped in pure acetone.
  8. Use an ultrasonic cleaning machine. These machines vibrate the coin rapidly to dislodge dirt. Small machines for home use are safe for coin cleaning, but will only remove soft, minor dirt buildup. Large, professional machines are more effective, but must be used carefully. For best results, suspend a cup from a string so it sits halfway submerged in the machine's bath, without touching the base. Fill the cup with slightly soapy distilled water and hang the coin suspended in this solution. Fill the main bath with pure distilled water, run the machine for only a few minutes, brush the coin, and repeat.[7]
    • You can run the machine without the cup, but dirt or objects on the base of the pan will interfere with the pan's vibration and shorten the machine's lifespan.

Harsh Cleaning Methods

  1. Use extreme caution with valuable coins. Cleaning a rare, collectible coin can reduce its value by over 50% due to tiny scratches or the removal of the tarnish. If the gentle cleaning methods above do not work, it's safer to have it cleaned professionally or accept an imperfect appearance. Feel free to use the methods below on common, non-collectible coins if you prefer a brighter appearance for your own collection.
    • An even gold, grey, or iridescent tarnish (toning) is desirable and increases the coin's value.[8]
    • A black or blotchy tarnish is not ideal, but harsh cleaning can still lower the value. Continue very carefully or take it to a professional.
  2. Pick dirt out of small crevices. After washing the coin in soapy water, you may still see dark areas outlining letters or detailed images. Wash again and pick away this dirt slowly and carefully using a toothpick or bamboo skewer. Take care not to scratch the coin, since the pick can scratch away the tarnish.[2]
    • Pointy plastic utensils are slower, but less likely to scratch the coin.
  3. Rub with silver polish. Silver polishes clean metal using acid and abrasives, both of which eat away a small layer of metal. This is an easy way to brighten non-collectible coins, but will almost certainly damage the value of collectibles:[9]
    • Put a coin-sized dollop of polish on a soft cloth.
    • Fold the cloth in half to transfer the polish to two sides.
    • Place the coin between the fold of cloth.
    • Rub together briefly.
    • Wipe off the coin on a clean part of the cloth.
  4. Wipe with a paste of baking soda and water. This cheaper alternative to silver polish also abrades the silver coin, causing scratches that will be visible under a magnifying glass. Minimize damage by using distilled water and mixing in just a little baking soda to make a watery paste. Dip the entire coin the paste, rub between your fingers for a minute, then rinse with water. Repeat two or three times if necessary. Pat dry.[9]
  5. Remove hard deposits with ammonium. A thick buildup on ancient coins is likely "horn silver" (silver chloride). This may be worth removing, especially if it prevents identification. Submerge the coin in a 10% ammonia solution in a tightly sealed container. Remove it after a few minutes, rinse immediately in water, then brush with a soft toothbrush. Repeat as needed.[10]
    • Warning: ammonia liquid and fumes are corrosive. Wear neoprene gloves and work in a ventilated area.[11]
    • Some hard buildups are the result of a different chemical reaction, which may require other treatments. Consult a coin dealer first if the coin might be valuable.
  6. Use extra-harsh treatments as a last resort. The following treatments are especially risky. Without expert supervision, they may remove the tarnish or pit the coin's surface. These are more often used on ancient coins, where heavy buildup may prevent identification or severely lower the value. Relatively modern, machine-made coins should only be treated this way if they have little collector's value and an unattractive tarnish:
    • Soak the coin in a 50/50 mix of distilled water and lemon juice for one hour.[12]
    • Soak the coin in 1 tsp (5 mL) lemon juice mixed into 1.5 cups (360 mL) olive oil. Warm this in a heat safe container inside a water bath, but keep it below boiling.[13]
    • "Dipping" treatments can return a coin to a frosty white silver appearance, which some collectors value. However, this is an extremely risky procedure that can cause blemishes to appear. Hiring a professional is strongly recommended, but you can buy a dipping solution to use at home.[8]

Tips

  • If your coin is coated in lacquer or covered in a slimy green substance (a reaction to PVC in certain plastics), remove them with pure acetone. Wipe off slime with a cotton swab dipped in the acetone. Remove lacquer by soaking the coin in acetone in a non-plastic container. Work in a ventilated area to protect against fumes, and keep the acetone away from fire and heat.[14] If the coin is valuable, take it to a professional instead.[15]
  • Uncirculated and well-preserved "proof" coins should have a bright, silver surface with no tarnish. Do not clean or handle these, since the lack of scratches and damage makes them valuable. Dust them with a squeeze bulb of air, not by rubbing them.[16]
  • Heavily corroded coins are usually too damaged to be worth saving, even after your remove the corrosion.[1]

Warnings

  • Do not be tempted to use metal tools on coins, as this can scratch the finish.
  • Be very careful with any coins which appear to be plated with missing plated areas, as soaking can make the bronze underneath the plating discolour the silver finish. Be patient.

Related Articles

Sources and Citations

  1. ↑ 1.0 1.1 1.2 1.3 1.4 http://www.numismaster.com/ta/inside_numis.jsp?page=how-to-handle-clean-coins
  2. ↑ 2.0 2.1 2.2 2.3 http://romancoin.info/complete_guide_to_uncleaned_ancient_coins.htm
  3. ↑ http://www.forumancientcoins.com/Articles/Uncleaned_Ancient_Coins.html
  4. ↑ http://www.kersh.com/coin_cleaning.php
  5. ↑ 5.0 5.1 http://www.metaldetectingworld.com/cleaning_coin_p6_mechanical.shtml
  6. ↑ 6.0 6.1 http://www.rhyniechert.com/coinscleaning.html
  7. ↑ http://www.metaldetectingworld.com/cleaning_coin_p14_ultrasonics.shtml
  8. ↑ 8.0 8.1 https://www.ngccoin.com/news/article/2831/dipping/
  9. ↑ 9.0 9.1 http://www.silverinvestingsimplified.com/Cleaning-Silver-Coins.html
  10. ↑ http://www.colchestertreasurehunting.co.uk/c/cleaning.htm
  11. ↑ https://www.osha.gov/SLTC/etools/ammonia_refrigeration/safety/
  12. ↑ http://ancientcoinsforeducation.org/content/view/66/90/
  13. ↑ http://www.metaldetectingworld.com/cleaning_coin_p13_ammonia.shtml
  14. ↑ https://www.buysilver.org/how-to-clean-coins/
  15. ↑ https://coins.thefuntimesguide.com/cleaning_coins/
  16. ↑ http://www.mycoincollecting.com/collecting/cleaning-coins.html

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