Ever looked at a dull, tarnished penny and wondered if there was an easy way to restore its shine? Baking soda, that ubiquitous white powder found in nearly every kitchen, often comes up as a potential solution. But does baking soda really clean pennies, and if so, how does it work? The answer is a resounding yes, with a caveat – the chemistry is a little more nuanced than simply sprinkling baking soda on a coin.
Understanding the Science Behind Tarnish on Pennies
Before we jump into the cleaning process, let’s understand why pennies get dull in the first place. Pennies minted after 1982 are primarily made of zinc with a thin copper plating. When exposed to air and moisture, the copper reacts with oxygen and other elements in the atmosphere, forming copper oxides and copper sulfides on the surface. This layer of corrosion is what we perceive as tarnish. This tarnish isn’t just dirt; it’s a chemical change to the metal itself.
The Chemical Reactions at Play
The primary culprit in penny tarnish is oxidation, where copper atoms lose electrons to oxygen atoms, forming copper oxide. This oxide layer dulls the copper’s natural luster. Another significant contributor is sulfur, which reacts with copper to form copper sulfide. Copper sulfide is often black or dark brown, further contributing to the unsightly appearance of tarnished pennies. The presence of acids in the environment, such as those from fingerprints or pollution, can accelerate these reactions.
Why Older Pennies Behave Differently
Pre-1982 pennies are almost entirely copper. While they still tarnish, the process can appear somewhat different due to the higher copper content. The thicker layer of copper means the tarnish might be more uniform and less likely to expose a different metal underneath. However, the same basic chemical reactions of oxidation and sulfidation are still at work.
Baking Soda as a Cleaning Agent: A Closer Look
Baking soda, or sodium bicarbonate (NaHCO3), is a mild alkali. It’s not a strong base like lye, but it’s alkaline enough to react with acids. This mild alkalinity is key to its cleaning ability. It can also act as a gentle abrasive.
The Role of Baking Soda in Removing Tarnish
Baking soda alone is not usually sufficient to remove heavy tarnish. It shines when combined with a weak acid. The most common combination is baking soda and vinegar (acetic acid). The acid dissolves some of the copper oxide and copper sulfide, while the baking soda neutralizes the acid and provides a mild abrasive action to help lift the loosened tarnish.
The Baking Soda and Vinegar Reaction: What Happens?
When baking soda and vinegar mix, they react to produce carbon dioxide gas (the fizzing you see), water, and sodium acetate. The carbon dioxide helps to agitate the solution and lift the tarnish, while the sodium acetate contributes to the cleaning process. However, the main cleaning action comes from the initial acidic environment created by the vinegar dissolving the tarnish. The baking soda helps to control the acidity, preventing excessive corrosion of the penny.
The Best Methods for Cleaning Pennies with Baking Soda
Several methods utilize baking soda for cleaning pennies, each with slight variations. These methods often include combinations with other household items.
The Classic Baking Soda and Vinegar Soak
This is a popular and effective method. Simply mix baking soda and vinegar to create a paste or solution.
- Make a paste by mixing equal parts baking soda and white vinegar in a small bowl.
- Apply the paste to the pennies, ensuring they are fully coated.
- Let the pennies soak for a few minutes (5-10 minutes is usually sufficient).
- Rinse the pennies thoroughly with water.
- Dry the pennies with a soft cloth.
For a solution, mix a tablespoon of baking soda with a cup of vinegar. Soak the pennies in the solution for a similar duration, then rinse and dry. The fizzing action of the baking soda and vinegar helps to loosen the tarnish.
Baking Soda Paste and Lemon Juice
Lemon juice contains citric acid, another weak acid that can dissolve tarnish. Combining it with baking soda creates a similar cleaning effect to the vinegar method.
- Create a paste by mixing baking soda with enough lemon juice to form a thick consistency.
- Apply the paste to the pennies.
- Let the pennies sit for 5-10 minutes.
- Rinse thoroughly with water.
- Dry the pennies with a soft cloth.
The citric acid in the lemon juice acts as the cleaning agent in this scenario, while the baking soda provides gentle abrasion.
Baking Soda and Water Scrub
For lightly tarnished pennies, a simple baking soda and water paste can be sufficient.
- Mix baking soda with a small amount of water to create a thick paste.
- Apply the paste to the pennies.
- Gently scrub the pennies with a soft cloth or toothbrush.
- Rinse thoroughly with water.
- Dry the pennies with a soft cloth.
This method relies primarily on the abrasive action of the baking soda to remove the tarnish. It’s less aggressive than the acid-based methods but can be effective for removing surface dirt and light oxidation.
Important Considerations and Potential Risks
While baking soda is generally safe to use, there are a few important considerations to keep in mind when cleaning pennies.
The Risk of Over-Cleaning and Damage
Prolonged exposure to acids, even weak ones like vinegar or lemon juice, can damage the copper plating on newer pennies or the surface of older, solid copper pennies. Avoid soaking pennies for extended periods (more than 15-20 minutes) and always rinse them thoroughly after cleaning. Excessive scrubbing can also scratch the surface of the coin.
Protecting Yourself and the Environment
While baking soda is non-toxic, it’s always a good idea to wear gloves when handling cleaning solutions. Avoid getting the solutions in your eyes or mouth. Dispose of the used cleaning solutions responsibly.
When Not to Clean Pennies
If you are dealing with rare or potentially valuable coins, it is strongly advised to consult with a professional numismatist before attempting to clean them. Cleaning valuable coins can significantly decrease their value. The natural patina that develops over time is often considered desirable by collectors. Harsh cleaning methods can remove this patina and leave the coin looking unnatural and damaged. Only clean common, low-value pennies that you intend to use for everyday transactions or simple experiments.
Alternative Penny Cleaning Methods
While baking soda is a popular option, other methods can also be used to clean pennies.
Commercial Coin Cleaners
Commercial coin cleaners are specifically formulated to remove tarnish without damaging the metal. These cleaners often contain a blend of chemicals designed to dissolve copper oxides and sulfides. Always follow the manufacturer’s instructions carefully when using commercial coin cleaners.
Other Household Items
Some people have success cleaning pennies with ketchup (which contains acetic acid) or Worcestershire sauce. The principles are similar to the baking soda and vinegar method – the acid dissolves the tarnish. However, these methods can be less predictable and potentially more damaging than baking soda.
The Final Polish: Achieving a Lasting Shine
Once the pennies are cleaned, it’s important to protect them from tarnishing again.
Drying and Sealing
Thoroughly drying the pennies after cleaning is crucial. Moisture can accelerate the tarnishing process. Use a soft, clean cloth to dry the pennies completely. You can also consider using a commercial coin sealant to protect the surface from oxidation and other environmental factors.
Proper Storage
Storing pennies in a dry, airtight container can help prevent them from tarnishing. Avoid storing pennies in humid environments or in contact with materials that can promote corrosion, such as cardboard or certain plastics. Coin collecting albums or holders designed specifically for coins are ideal for long-term storage.
Does baking soda scratch pennies during the cleaning process?
Baking soda itself is a very mild abrasive, and when used with a soft cloth or sponge, it’s unlikely to cause significant scratches on pennies. However, the dirt and grime embedded on the coin’s surface are the primary culprits for potential scratching. These abrasive particles are dislodged by the baking soda and rubbing action, which can lead to micro-scratches if you’re not careful. The hardness of the cleaning implement used also plays a role; a rough cloth will undoubtedly cause more abrasion than a very soft one.
To minimize the risk of scratching, it’s crucial to rinse the penny frequently during the cleaning process to remove dislodged particles. Employing gentle pressure and circular motions with a soft, lint-free cloth is also recommended. Avoid using abrasive sponges or brushes. Ultimately, the goal is to lift the tarnish and dirt rather than forcefully scrub the surface, thus preserving the coin’s original details.
Why does baking soda help clean pennies? What’s the chemical reaction involved?
The cleaning action of baking soda on pennies stems from its mild abrasive properties and its ability to react with acids. Tarnish on pennies is primarily composed of copper oxides and sulfides, which can be partially removed by the gentle scrubbing action of baking soda. The abrasive effect helps to physically dislodge loose dirt and tarnish particles from the coin’s surface, making it appear brighter.
While baking soda itself is alkaline, the typical cleaning process involves mixing it with an acid like vinegar (acetic acid) or lemon juice (citric acid). When baking soda (sodium bicarbonate) reacts with an acid, it produces carbon dioxide gas, water, and a salt. This reaction helps to dissolve some of the copper oxide and sulfide compounds, further facilitating their removal. The resulting solution can then be easily rinsed away, leaving behind a cleaner penny.
Is it safe to use baking soda to clean all types of coins?
While baking soda can be effective for cleaning pennies and other copper-based coins, it’s generally not recommended for cleaning all types of coins, especially those made of more delicate metals like silver or gold. The mild abrasive nature of baking soda, even when used gently, can potentially damage the surface of softer metals, leading to scratches or the removal of a coin’s patina.
For precious metal coins, it’s best to consult with a numismatist or coin collecting expert before attempting any cleaning methods. They can provide guidance on safe and appropriate cleaning techniques that won’t harm the coin’s value or appearance. Generally, mild soap and water are often the safest approach for cleaning these types of coins.
Will cleaning pennies with baking soda affect their collectible value?
Cleaning coins, including pennies, can significantly impact their collectible value, especially for older or rare coins. Collectors generally prefer coins with their original patina, which is the natural toning that occurs over time due to oxidation and environmental exposure. Cleaning removes this patina, making the coin look artificial and potentially lowering its numismatic value.
While a cleaned coin might look “better” to the untrained eye, experienced collectors typically devalue coins that have been cleaned, as it indicates tampering and alters the coin’s historical character. In some cases, aggressive cleaning can even cause irreversible damage, such as scratches or a dull, lifeless appearance, further diminishing the coin’s worth. It is generally advised to avoid cleaning collectible coins unless you have expert knowledge and a specific reason to do so.
What is the best way to mix baking soda for cleaning pennies?
The most common and effective method is to create a paste by mixing baking soda with a small amount of water or vinegar. Start with a tablespoon of baking soda in a small bowl and gradually add the liquid until you achieve a thick, creamy consistency. The paste should be easily spreadable but not too runny. Adding a few drops of lemon juice can also enhance the cleaning power, especially for heavily tarnished pennies.
Alternatively, you can sprinkle baking soda directly onto a damp cloth or sponge. Gently rub the penny with the baking soda, ensuring that you cover the entire surface. After scrubbing for a short period, rinse the penny thoroughly with clean water to remove any residue. Remember to use soft materials and avoid excessive pressure to prevent scratching.
How long should I leave baking soda on a penny to clean it effectively?
The ideal soaking time depends on the level of tarnish present on the penny. For lightly tarnished pennies, a brief contact time of just a few seconds to a minute may be sufficient. Heavily tarnished pennies might require a longer soak, but it’s best to start with a shorter duration and gradually increase it as needed to avoid over-cleaning or potential damage.
It’s crucial to monitor the cleaning process closely and regularly check the penny’s appearance. Remove the penny from the baking soda paste or solution as soon as you observe the desired level of cleaning. Over-soaking can sometimes lead to discoloration or other undesirable effects. After removing the penny, rinse it thoroughly with clean water and pat it dry with a soft cloth.
Are there any precautions I should take when cleaning pennies with baking soda?
Always wear gloves to protect your hands from prolonged contact with baking soda and any cleaning solutions used. While baking soda is generally considered safe, extended exposure can cause skin irritation for some individuals. Also, ensure that the area where you’re cleaning the pennies is well-ventilated, especially if you’re using vinegar or other chemicals alongside the baking soda.
Avoid getting baking soda or cleaning solutions into your eyes. If contact occurs, rinse your eyes thoroughly with water for several minutes and seek medical attention if irritation persists. Finally, be mindful of the surfaces you’re working on, as some cleaning solutions can damage certain materials. It’s best to work on a non-porous surface or protect your workspace with a plastic sheet or newspaper.