Verdigris and PVC: Saving Your Coins from Environmental Damage Before You Sell

Improper storage is the silent enemy of numismatics. Let’s identify the signs of environmental damage specific to this metal type.

As a numismatic conservator with decades of experience examining, preserving, and grading coins, I can tell you that one of the most heartbreaking things I encounter is a coin that has been destroyed — not by time, but by neglect. Whether you are preparing a collection for sale on eBay, shipping a $3,000 piece to Great Collections, or simply trying to preserve inherited coins for the next generation, understanding environmental damage is absolutely critical. The difference between a coin that commands top dollar and one that is essentially worthless often comes down to how it was stored.

In this guide, I will walk you through the most common forms of environmental damage I see in my conservation work — bronze disease, PVC plasticizer damage, and oxidation — and I will explain the proper chemical conservation techniques, including acetone dips, that every collector and seller should understand. If you are planning to sell coins, especially raw or ungraded pieces, knowing these factors will not only protect your investment but will also help you accurately describe your listings and avoid costly disputes with buyers.

Understanding the Enemies: What Environmental Damage Actually Looks Like

Before we discuss remedies, we need to understand what we are fighting. Environmental damage to coins manifests in several distinct forms, and each one tells a story about how the coin was stored and what it was exposed to. In my experience grading and conserving coins, I have seen every variation of these problems, from subtle early-stage corrosion to catastrophic destruction that renders a coin completely unsalvageable.

Bronze Disease: The Silent Killer

Bronze disease is, without exaggeration, one of the most destructive and insidious forms of corrosion that affects copper-based coins — including bronze, brass, and even some copper-nickel compositions. Despite its name, it is not a biological condition. It is an electrochemical reaction caused by the interaction of copper chlorides in the alloy with moisture and oxygen.

What makes bronze disease so dangerous is that it is self-perpetuating. Once it begins, it creates hydrochloric acid as a byproduct, which attacks more copper in the coin, which creates more copper chlorides, which react with more moisture — and the cycle continues indefinitely. I have examined coins that were perfectly healthy when placed in a collection and returned to find them covered in bright green, crusty pitting just a few years later.

Signs of bronze disease include:

• Small, bright green spots or raised bumps on the coin’s surface
• A powdery or crusty texture that cannot be easily wiped away
• Pitting beneath the green deposits — this is where the actual metal loss occurs
• Spreading patterns that grow over time, even in seemingly dry conditions

If you are preparing coins for sale and you notice any of these signs, you need to disclose them in your listing. Buyers — especially experienced numismatists — will look for bronze disease, and failure to disclose it is one of the fastest ways to receive a return request or negative feedback on eBay.

PVC Plasticizer Damage: The Hidden Threat in Your Flips

Polyvinyl chloride — commonly known as PVC — has been used in coin flips, holders, and storage pages for decades. Many collectors still use PVC-based products without realizing the damage they cause. The problem is that PVC contains plasticizers (chemicals added to make the plastic flexible) that off-gas over time, especially in warm or humid environments. These gases react with the metal surface of coins, creating a distinctive greenish or hazy film.

I have examined thousands of coins stored in PVC flips, and the damage ranges from a light, hazy green tint that can sometimes be reversed to deep, sticky corrosion that has permanently etched the coin’s surface. The severity depends on several factors:

• Duration of exposure: Coins stored in PVC for decades almost always show significant damage.
• Temperature: Warm storage environments accelerate the off-gassing process dramatically.
• Humidity: Moisture amplifies the chemical reaction between PVC gases and the coin’s surface.
• Metal type: Copper and bronze coins are most susceptible, but silver and gold can also be affected.

How to identify PVC damage:

• A greenish, sometimes sticky or waxy film on the coin’s surface
• Haze or cloudiness that does not wipe off with a soft cloth
• A distinctive chemical smell when you open the holder (PVC has a characteristic plastic odor)
• Damage that is often more pronounced on the side of the coin that was in direct contact with the flip

If you are selling coins that have been stored in PVC flips, I strongly recommend removing them and replacing them with Mylar or archival-quality holders before listing. This simple step can significantly improve the appearance and perceived value of your coins.

Oxidation and Tarnish: The Most Common (and Most Misunderstood) Issue

Oxidation is the broad term for the chemical reaction between a metal and oxygen. In numismatics, we typically refer to the result as tarnish (on silver), toning (on various metals), or patina (on copper and bronze). Unlike bronze disease and PVC damage, oxidation is not always a bad thing. In fact, many collectors actively seek out coins with attractive, original toning.

However, oxidation becomes a problem when it is:

• Uneven or blotchy: Heavy, irregular tarnish can obscure design details and reduce a coin’s eye appeal and grade.
• Corrosive: Some forms of oxidation, particularly on copper-based coins, can progress beyond surface discoloration into actual metal loss.
• Artificially induced: Coins that have been artificially toned or “dipped” excessively often show unnatural colors or a washed-out appearance that experienced collectors and graders can easily detect.

In my experience, the most common oxidation-related mistake I see sellers make is over-cleaning. Desperate to make a tarnished coin look more appealing, sellers will dip it in harsh chemical solutions or even attempt mechanical cleaning with abrasive materials. This almost always does more harm than good. A coin with original, even tarnish is almost always worth more than a coin that has been stripped of its original surface.

Proper Chemical Conservation: What Works and What Doesn’t

When it comes to conservation, the guiding principle should always be do no harm. Professional numismatic conservators follow a strict hierarchy of intervention, starting with the least invasive methods and only escalating when necessary. Here is what I recommend for common conservation scenarios.

Acetone Dips: The Gold Standard for Organic Residue Removal

Pure acetone (the solvent, not nail polish remover which contains additives) is one of the safest and most effective conservation tools available to collectors. Acetone is an excellent solvent for organic compounds — it will dissolve PVC residue, adhesive from tape, oils from fingerprints, and other organic contaminants without reacting with the metal itself.

How to perform a proper acetone dip:

1. Use 100% pure acetone from a hardware store. Do not use nail polish remover, as it contains oils, fragrances, and other additives that can leave a residue on the coin.
2. Work in a well-ventilated area away from any open flame. Acetone is highly flammable.
3. Place the coin in a glass or ceramic container and pour enough acetone to fully submerge it.
4. Allow the coin to soak for no more than 30 seconds to a few minutes, depending on the severity of the contamination.
5. Remove the coin with tweezers (not your fingers) and allow it to air dry on a clean, lint-free cloth. Do not rinse with water.
6. For heavy PVC residue, you may need to gently roll (not rub) a cotton swab across the surface while the coin is still wet with acetone.

Important warnings:

• Acetone will not remove toning, patina, or oxidation from a coin. If someone tells you an acetone dip will make a tarnished silver coin look like new, they are mistaken.
• Acetone will not cure bronze disease. Bronze disease requires specialized treatment (which I will discuss below).
• Never use acetone on coins with artificial toning or coatings that you want to preserve — it may strip them away.

Treating Bronze Disease: A Delicate Process

Bronze disease requires a more aggressive approach than simple acetone dips. The goal is to remove all copper chlorides from the coin’s surface and then seal the coin to prevent recurrence. Here is the process I use in my conservation work:

1. Mechanical removal: Under magnification, use a wooden toothpick or a fine bamboo skewer to gently remove the visible green crust. Be careful not to scratch the coin’s surface. This step removes the bulk of the corrosion products but does not eliminate the copper chlorides embedded in the metal.
2. Chemical treatment: Soak the coin in a 5% sodium sesquicarbonate solution for several hours to several days, depending on the severity. This solution converts the copper chlorides to stable copper compounds. Monitor the process closely — the solution will turn blue-green as it draws the chlorides out of the coin.
3. Rinse thoroughly: After treatment, rinse the coin in multiple changes of distilled water to remove all traces of the chemical solution.
4. Dry completely: Allow the coin to dry thoroughly in a warm, dry environment. Any remaining moisture can restart the bronze disease cycle.
5. Seal the surface: Apply a thin coat of Incralac or a similar lacquer specifically designed for copper alloys. This creates a barrier against moisture and oxygen.

I want to emphasize that bronze disease treatment is not a beginner-level conservation technique. If you have a valuable coin showing signs of bronze disease, I strongly recommend consulting a professional conservator rather than attempting treatment yourself. Improper treatment can cause irreversible damage.

What NOT to Do: Common Conservation Mistakes

Over my career, I have seen more coins destroyed by well-meaning cleaning than by any other cause. Here are the practices I urge you to avoid:

• Never use abrasive cleaners: Products like Brasso, silver dip, or baking soda paste will strip the original surface of the coin and leave microscopic scratches that are visible under magnification. These coins will almost always be details-graded as “cleaned” by PCGS or NGC, dramatically reducing their numismatic value.
• Never rub or polish a coin: Even soft cloths can cause hairline scratches on a coin’s surface. The original mint luster — the undisturbed flow lines of metal from the striking process — is one of the most important factors in determining a coin’s grade and collectibility.
• Never use vinegar, lemon juice, or other acids: These will react aggressively with most coin metals and can cause severe, irreversible damage in seconds.
• Never attempt to “improve” toning: Artificial toning is easily detected by experienced graders and will result in a details grade. Original toning, even if uneven, is always preferable.

Proper Storage: Prevention Is Always Better Than Cure

The best way to deal with environmental damage is to prevent it from happening in the first place. Proper storage is not expensive or complicated, but it requires attention to a few key principles.

Choosing the Right Holders

Every coin in your collection should be stored in an archival-quality holder. Here are my recommendations:

• Mylar flips (also called “soft flips”): These are the standard for individual coin storage. They are chemically inert and will not react with the metal. Brands like Capital Plastics and Lighthouse produce excellent Mylar flips.
• Archival cardboard 2x2s with Mylar windows: These are ideal for coins you plan to sell, as they allow the buyer to view the coin without handling it directly.
• Air-tight capsules: For higher-value coins, air-tight capsules made from inert plastics provide an additional layer of protection against humidity and airborne contaminants.
• PCGS/NGC/ANACS slabs: Professionally graded and encapsulated coins are already in archival-quality holders. Do not remove them from their slabs.

Never use:

• PVC flips or holders (as discussed above)
• Paper envelopes (paper contains sulfur compounds that can tarnish silver)
• Rubber bands (rubber contains sulfur and will cause severe tarnish)
• Any container that smells strongly of chemicals or plastic

Controlling the Storage Environment

Even the best holders cannot fully protect coins in a hostile environment. Here are the environmental factors you need to control:

• Humidity: Keep relative humidity below 50%. Ideally, aim for 30-40%. Use silica gel packets in your storage area, and replace or recharge them regularly. I have seen entire collections develop bronze disease after being stored in a humid basement for just one summer.
• Temperature: Store coins in a cool, stable environment. Avoid attics, garages, and any location with significant temperature fluctuations. Temperature changes cause condensation, which accelerates corrosion.
• Air quality: Avoid storing coins near sources of chemical fumes, including household cleaners, paints, and solvents. Even cooking fumes (particularly from frying, which releases sulfur compounds) can tarnish silver coins over time.
• Light: Prolonged exposure to direct sunlight can cause uneven toning on some coins. Store coins in a dark environment when not being viewed.

Preparing Coins for Sale: A Conservator’s Checklist

If you are preparing to sell coins — whether on eBay, through a dealer, or at auction — proper conservation and presentation can make a significant difference in the price you receive. Here is the checklist I recommend:

1. Inspect each coin under magnification: Use a 5x to 10x loupe to examine both sides of every coin. Look for signs of bronze disease, PVC damage, cleaning, or other issues that need to be disclosed.
2. Remove coins from PVC holders: If any coins are stored in PVC flips, transfer them to Mylar holders immediately. If PVC residue is present, perform an acetone dip as described above.
3. Do NOT clean the coins: Unless you are dealing with surface contamination (adhesive, PVC residue, etc.), leave the coins as they are. Original surfaces are always more valuable than cleaned surfaces.
4. Take high-quality photographs: Use a neutral background, consistent lighting, and a macro lens or close-up setting. Photograph both sides of the coin and any notable features (toning, marks, etc.). Accurate photos reduce the likelihood of returns and disputes.
5. Describe the coin accurately: Disclose any known issues, including environmental damage. Buyers appreciate honesty, and accurate descriptions protect you from returns and negative feedback.
6. Package securely for shipping: Use archival-quality holders, secure packaging, and appropriate insurance. For high-value coins, USPS Registered Mail provides the highest level of security.

Case Study: The Impact of Environmental Damage on Value

To illustrate just how dramatically environmental damage can affect a coin’s value, let me share a case from my own conservation practice. I was recently asked to examine a 1921 Morgan silver dollar that the owner had purchased at an estate sale. The coin was stored in a PVC flip for what appeared to be several decades.

Upon examination, I found:

• Heavy PVC residue on both sides, creating a greenish, hazy film
• Sticky corrosion in the recesses of the design, particularly around the lettering and date
• Evidence of attempted cleaning — someone had tried to wipe away the PVC residue with a cloth, leaving fine hairline scratches across the obverse

The coin, which might have graded MS-63 or better in its original state, was now a details coin — “cleaned” with PVC damage. Its value dropped from an estimated $75-$100 for a straight-graded coin to perhaps $25-$30 as a details piece. A few decades of improper storage had cost the owner 60-70% of the coin’s value.

This is not an unusual case. I see variations of this story every week. The tragedy is that it is entirely preventable.

Conclusion: Protecting Your Numismatic Heritage

Environmental damage — whether from bronze disease, PVC plasticizer off-gassing, improper oxidation, or misguided cleaning attempts — is one of the greatest threats to the value and integrity of any coin collection. The good news is that it is almost entirely preventable with proper storage and handling.

As a numismatic conservator, my strongest advice is this: respect the original surface of every coin. That surface is a historical artifact — it carries the evidence of the coin’s journey from the mint to the present day. Every scratch, every spot of corrosion, every hint of toning tells a story. Our job as collectors, sellers, and stewards of these objects is to preserve that story, not to erase it.

If you are preparing coins for sale, take the time to inspect them carefully, store them properly, and describe them honestly. Your buyers will thank you, your coins will thank you, and the numismatic community will be better for it. And if you encounter a coin with significant environmental damage — particularly bronze disease — consider consulting a professional conservator before attempting any treatment. The right intervention can save a coin; the wrong one can destroy it.

The coins in your hands today are part of our shared cultural heritage. Treat them with the care they deserve, and they will reward you — both financially and historically — for generations to come.

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