Polishing coins, especially valuable or collectible ones, requires careful consideration. While one might want to restore their shine, harsh cleaning methods can damage a coin’s surface and significantly reduce its value. Many collectors appreciate the natural patina and toning that develops over time, as it tells a story and can even enhance a coin’s appeal. This article provides guidance on how to polish coin responsibly, focusing on gentle methods and important cautions.
When to Clean and When to Avoid Cleaning
The decision to clean a coin is a critical one, heavily dependent on the coin’s value, historical significance, and original condition.
- For collectible or antique coins, it is generally best to avoid cleaning them personally. Any attempt to clean these items without expert knowledge can irreversibly damage their surface, compromising their historical integrity and monetary value. Always consult with a professional numismatist or coin grader for guidance. These experts can assess the coin’s condition and recommend appropriate preservation methods, which rarely involve cleaning.
- Cleaning should only be considered for low-value coins or for specific purposes, like removing dirt or grime from everyday pocket change. This type of cleaning is primarily for aesthetic reasons or to remove surface contaminants that might obscure details. For instance, a coin found in the garden might benefit from a gentle clean to reveal its denomination or date. Real Simple magazine suggests that cleaning is only appropriate for items where value preservation is not a primary concern.
Understanding Coin Surfaces and Patina
Before discussing how to polish coin, it’s important to understand what you’re dealing with. Coins are made from various metals and alloys, including copper, silver, gold, nickel, and various combinations. Each metal reacts differently to environmental factors, leading to unique surface changes over time.
- Patina: This is a thin layer that forms on the surface of copper, bronze, and similar metals due to oxidation and other chemical reactions. It’s often green or brown and is highly valued by collectors as it indicates authenticity and age. Removing patina can drastically devalue a coin.
- Toning: This refers to the natural discoloration that occurs on silver and other metals due to exposure to air and pollutants, such as sulfur. Toning can appear in a range of colors, from subtle gold to vibrant rainbow hues. Like patina, natural toning is often desirable and can increase a coin’s value.
- Original Mint Luster: This is the shine a coin has when it is first struck. Over time, handling and environmental exposure diminish this luster. Once lost, it cannot be truly restored through cleaning without altering the coin’s surface.
Cleaning, especially abrasive cleaning, can strip away these natural layers, leaving a coin with an unnatural, “cleaned” look that is easily identifiable by experts and often results in a significant reduction in market value.
Gentle Methods for Low-Value Coins
If you choose to clean coins that are not valuable or collectible, here are some gentle methods. These methods aim to remove surface dirt and grime without resorting to harsh chemicals or abrasive materials. The goal is to improve the coin’s appearance slightly, not to achieve a “like-new” polish, which is usually detrimental.
1. Distilled Water Rinse and Air Dry
This is the safest and most recommended first step for any low-value coin with loose dirt.
- Procedure: Gently rinse the coin under a light stream of distilled water. Distilled water is preferred over tap water because it lacks minerals and chemicals that can leave deposits or react with the coin’s surface.
- Drying: After rinsing, allow the coin to air dry naturally on a soft, lint-free cloth, such as a microfiber cloth.
- Caution: Avoid rubbing the coin, as even soft cloths can scratch the surface, especially if there are still fine grit particles present. Air drying prevents scratches that can occur from wiping.
2. Soapy Water Soak
For more persistent dirt or grime that a simple rinse cannot remove, a gentle soak can be effective.
- Materials: A bowl, warm distilled water, and a squirt of mild, non-abrasive dish soap (e.g., plain Dawn or similar, free of lotions or strong detergents).
- Procedure: Fill a bowl with warm distilled water and add a small amount of dish soap. Place the coin in the solution and allow it to soak for a few minutes to several hours, depending on the amount of dirt. The soap helps to break down oils and loosen grime.
- Gentle Cleaning: After soaking, gently rub the coin between your fingers while it is still submerged in the soapy water to loosen dirt or grit. Do not use a brush or cloth at this stage.
- Rinsing: Rinse the coin thoroughly with clean distilled water to remove all soap residue.
- Drying: Pat the coin dry with a soft, lint-free cloth or allow it to air dry.
3. Baking Soda Paste
For more stubborn dirt or light tarnish on non-collectible coins, a baking soda paste can be used with extreme caution. Baking soda is a mild abrasive, so this method carries a higher risk of microscopic scratches. This method is a step towards how to polish coin slightly, but it’s more about cleaning.
- Materials: Baking soda, a small amount of distilled water, a soft cloth or a very soft-bristled toothbrush (like a baby’s toothbrush).
- Procedure: Create a paste by mixing baking soda with a small amount of distilled water until it reaches a consistency similar to toothpaste. Apply the paste to the coin using a soft cloth or the very soft-bristled toothbrush.
- Gentle Application: Gently rub the surface of the coin with the paste. Use minimal pressure and circular motions. Focus on areas with visible dirt or tarnish.
- Rinsing: Rinse the coin thoroughly with distilled water to remove all baking soda residue.
- Drying: Pat dry with a soft cloth or air dry.
- Caution: Baking soda can be abrasive, so use caution, especially on more delicate coins or those with intricate details. This method is not recommended for proof coins or coins with high luster.
4. Lemon Juice and Salt Solution (for Copper Coins)
This method is specifically for tarnished copper coins and is significantly more aggressive than the previous methods. It involves a mild acid and an abrasive, making it suitable only for very low-value copper coins where appearance is prioritized over long-term preservation. This is a common method when people ask how to polish coin that is copper.
- Materials: 1/4 cup (59 ml) of white distilled vinegar, 1 teaspoon (7 grams) of table salt, a non-metallic bowl, paper towels, cool water, and a soft towel.
- Procedure: In a non-metallic bowl, mix the white distilled vinegar with the table salt. Place the copper coin(s) into the solution and allow them to soak for approximately 5 minutes. The acid in the vinegar reacts with the copper oxides, and the salt acts as a mild abrasive to aid in tarnish removal.
- Cleaning: After soaking, gently wipe the coins with a paper towel to remove the loosened tarnish.
- Rinsing: Rinse the coins thoroughly with cool water to neutralize the acid and remove all salt residue.
- Drying: Dry them immediately and thoroughly with a soft towel to prevent new tarnish from forming.
- Caution: While effective for removing tarnish, salt can be abrasive and may leave microscopic scratches on the coin’s surface, especially if rubbed too vigorously. The acidic nature of vinegar can also strip away desirable patina and leave the copper with an unnaturally bright, “cleaned” appearance that can re-tarnish quickly. Use extreme caution and only on coins where surface integrity is not a concern.
Important Considerations and Cautions
When considering how to polish coin or clean any coin, understanding what not to do is as important as knowing what to do. The following cautions are paramount for preserving a coin’s integrity and value.
- Avoid Harsh Chemicals and Abrasive Materials:
- Strong Acids: Substances like concentrated vinegar, ketchup, or commercial cleaning acids can strip away a coin’s natural protective layer, dissolve metal, and cause irreversible corrosion. They can also leave behind residues that continue to damage the coin over time.
- Abrasive Materials: Scouring pads, steel wool, even stiff-bristled toothbrushes, can leave visible scratches on a coin’s surface. These scratches are permanent and significantly reduce the coin’s appeal and value. Even soft cloths can scratch if there are abrasive particles on the coin or cloth.
- Polishes: Commercial metal polishes (e.g., silver polish, brass polish) contain fine abrasives and chemicals designed to remove tarnish by sacrificing a layer of the metal. While they might make a coin shiny, they destroy the original surface and any valuable patina or toning.
- Do Not Use Silver Polish on Silver Coins: This is a common mistake. While silver polish removes tarnish, it does so by abrading the surface of the silver. For collectible silver coins, this results in an unnatural, “over-cleaned” appearance that is highly undesirable to collectors. It removes the natural luster and any desirable toning.
- Avoid Ultrasonic Cleaners: While seemingly gentle, ultrasonic cleaners can be detrimental to coins. They work by creating microscopic bubbles that implode, dislodging dirt. However, this process can also cause micro-abrasions on the coin’s surface, especially on softer metals or coins with delicate features. They can also dislodge existing toning or patina in an uneven way.
- Never “Dip” Collectible Coins: Coin “dips” are chemical solutions designed to quickly remove tarnish. While they work, they often leave coins with an unnatural, dull finish and can remove desirable toning, permanently damaging the coin’s surface and reducing its value.
- Handle Coins by Their Edges: Whenever you handle a coin, especially after cleaning, always hold it by its edges between your thumb and forefinger. Avoid touching the obverse (front) and reverse (back) surfaces, as oils and acids from your skin can leave fingerprints that will eventually tarnish or corrode the coin’s surface.
- If in Doubt, Consult with a Professional: This is the most important piece of advice. A numismatist or coin grader possesses the expertise to assess your coins accurately. They can provide expert advice on the best way to care for them, preserve their value, and determine if any cleaning (which is rare for valuable coins) is appropriate. They can also identify if a coin has already been improperly cleaned, which affects its market value. Professionals prioritize preservation over superficial shine.
By following these guidelines and exercising extreme caution, you can help preserve the integrity and beauty of your coins, whether they are cherished collectibles or everyday pocket change. The goal is to maintain their condition, not to achieve an artificial shine that compromises their authenticity and value.
How to quickly polish coins?
I can help with that. Add a small amount of water to a tablespoon of baking soda to form a paste. Apply the paste to each coin using an old toothbrush and scrub gently. Rinse the coins to reveal the now-shiny surfaces.