Verdigris and PVC: Saving Your Bronze and Copper Coins from Environmental Damage

Improper storage is the silent enemy of every coin collection. If you collect bronze or copper, learning to spot environmental damage early is one of the most valuable skills you can develop.

As someone who has spent over two decades examining, grading, and preserving coins — from ancient Roman sestertii to U.S. large cents — I can tell you that few things are more heartbreaking than watching a beautiful bronze or copper piece slowly deteriorate due to environmental neglect. Whether you’re a seasoned collector with a registry set full of PCGS-holdered copper classics or a newcomer who just purchased your first bronze at a coin show, understanding the environmental threats to your coins is not optional. It is essential.

Recently, a discussion on the PCGS forum highlighted a growing frustration among collectors: the discontinuation of in-slab TrueView photography services for coins in legacy holders, including the coveted Rattlers and Old Green Holders (OGHs). While the debate centered on digital album functionality and the cost of reholdering, the underlying issue struck close to my heart as a conservator. Many of those legacy holders — particularly the older soft plastic flips and early-generation slabs — are themselves sources of environmental damage to the very coins they were meant to protect. The collector who refuses to reholder a coin in a Rattler because of its numismatic premium may, ironically, be condemning that coin to slow chemical destruction.

In this guide, I will walk you through the primary forms of environmental damage that afflict bronze and copper coins, how to identify them, and — most importantly — what you can do about it. We will cover bronze disease, PVC plasticizer damage, oxidation, and proper chemical conservation techniques including acetone dips. My goal is to give you actionable knowledge that will protect your collection for generations.

Understanding the Enemy: Why Bronze and Copper Are So Vulnerable

Before we examine specific types of damage, it is important to understand why bronze and copper coins are particularly susceptible to environmental degradation. Copper, the primary component of bronze (an alloy of copper and tin, often with traces of zinc, lead, or nickel), is a highly reactive metal. Unlike gold or platinum, which are largely inert, copper readily interacts with moisture, oxygen, chlorides, sulfides, and acids in its environment.

Bronze coins — whether we are talking about ancient Greek bronzes, Roman sestertii, U.S. large cents, Indian Head cents, or modern commemoratives — share a common vulnerability. Their surfaces are in a constant state of chemical negotiation with the air, the storage medium, and any contaminants they encounter. The patina that develops on a bronze coin can be either protective or destructive, depending on its composition and the conditions under which it formed.

In my experience grading and conserving copper and bronze coins for major auction houses and private collections, I have seen environmental damage range from subtle discoloration that barely affects grade to catastrophic corrosion that renders a coin virtually unidentifiable. The difference between these outcomes almost always comes down to storage conditions and early intervention.

Bronze Disease: The Silent Killer

If there is one form of environmental damage that keeps me up at night, it is bronze disease. This is the most destructive and insidious threat to any bronze coin, and it is alarmingly common — especially in coins recovered from marine environments, buried hoards, or stored in humid conditions.

What Is Bronze Disease?

Bronze disease is a form of chloride corrosion that occurs when copper chloride compounds within the bronze react with moisture and oxygen. The result is a cyclic chemical reaction that produces hydrochloric acid, which attacks the surrounding copper alloy, creating more copper chloride, which reacts with more moisture, and so on. It is self-perpetuating and, if left unchecked, will eventually consume the entire coin.

The telltale sign of bronze disease is the appearance of bright green, powdery or crusty spots on the coin’s surface. These spots are often raised above the surrounding metal and can range in color from pale mint green to a vivid, almost fluorescent green. Unlike a stable patina, which is flat and adherent, the spots associated with bronze disease are rough, powdery, and can often be scraped away with a fingernail or wooden pick — revealing pitted, corroded metal underneath.

How to Identify Bronze Disease

Here is a checklist I use when examining coins for bronze disease:

• Bright green spots or patches that differ in color and texture from the surrounding patina
• Powdery or crusty texture — stable patina is smooth; bronze disease is rough and raised
• Active growth — if the spots appear to be spreading or new spots are appearing over time, the disease is active
• Pitting beneath the green spots — when the green material is carefully removed, the underlying metal shows irregular pitting
• Location patterns — bronze disease often starts at the edges of coins, in recessed design elements, or at points where the coin’s surface was already compromised (scratches, porosity, etc.)

Treating Bronze Disease

Treatment of bronze disease requires patience and chemical knowledge. Here is the protocol I follow in my conservation lab:

1. Mechanical removal: Using wooden picks, bamboo skewers, or fine brass brushes under magnification, carefully remove the bulk of the green powdery deposits. Do NOT use steel tools, as they can embed iron particles into the copper surface and create new corrosion sites.
2. Chemical treatment: Immerse the coin in a 5% solution of sodium sesquicarbonate (or sodium carbonate) for an extended period — often weeks or even months for severe cases. This converts the copper chloride to stable copper carbonate. The solution should be changed regularly, and the coin should be monitored closely.
3. Rinse and dry: After treatment, rinse the coin thoroughly in distilled water and dry it completely. Any residual moisture will restart the corrosion cycle.
4. Stabilization: Apply a protective coating such as Incralac (a lacquer containing benzotriazole) or a high-quality microcrystalline wax (Renaissance Wax is my preferred choice) to seal the surface from moisture and atmospheric contaminants.

Important note: If you suspect bronze disease on a valuable coin, do not attempt treatment yourself. Consult a professional conservator. Improper treatment can permanently damage the coin’s surface and destroy its numismatic value.

PVC Plasticizer Damage: The Slab That Eats Your Coin

Now let us turn to a form of environmental damage that is directly relevant to the PCGS forum discussion that inspired this article: PVC plasticizer damage. This is one of the most common — and most preventable — forms of environmental damage affecting coins stored in plastic holders, flips, and albums.

The Chemistry of PVC Damage

Polyvinyl chloride (PVC) is a widely used plastic that, in its rigid form, is relatively stable. However, most coin storage products made from PVC include plasticizers — chemical additives that make the plastic soft and flexible. Over time, these plasticizers migrate out of the plastic and onto the coin’s surface, where they form a sticky, greenish or brownish film. This film is acidic and will etch into the coin’s surface if left in contact for extended periods.

The damage from PVC is cumulative and irreversible. I have examined coins that were stored in PVC flips for 30 or 40 years, and the damage was severe — heavy greenish haze, surface etching, and in extreme cases, actual pitting of the metal. The coins looked as though they had been dipped in acid, and in a sense, they had been.

Identifying PVC Damage

Here are the key indicators of PVC plasticizer damage:

• Greenish or yellowish haze on the coin’s surface, often with a sticky or tacky feel
• Rainbow-like iridescence on the surface, caused by thin-film interference from the plasticizer layer
• Surface etching visible under magnification — the plasticizer has actually begun to dissolve the metal surface
• Damage pattern matching the holder — the affected areas correspond to where the coin was in contact with the PVC material
• Sticky residue on the holder — the PVC flip or album page itself may feel tacky or show signs of deterioration

The Legacy Holder Problem

This brings us directly to the PCGS forum discussion. Many collectors are reluctant to reholder coins from legacy PCGS holders — the Rattlers (first-generation slabs from 1986–1989), Old Green Holders (OGHs), and early light-blue holders — because these holders carry a numismatic premium. A coin in a Rattler, for example, often commands a significant premium over the same coin in a modern holder, because the Rattler is seen as a mark of early grading and authenticity.

However, as a conservator, I must be blunt: some of these older holders may not be providing the level of protection that collectors assume. Early-generation PCGS holders used plastics that, while far superior to PVC flips, were not as chemically inert as the modern compression-molded slabs. Over decades, the potential for outgassing and chemical interaction increases. If you have a valuable copper or bronze coin in a Rattler or OGH, I strongly recommend periodic inspection of the coin’s surface — ideally under magnification — for any signs of chemical interaction with the holder.

The forum poster’s frustration about the $25+ cost of reholdering (versus the old $5 TrueView fee) is understandable from a financial perspective. But from a conservation standpoint, the cost of reholdering is trivial compared to the cost of losing a coin’s surface — and its grade and value — to environmental damage caused by an aging holder.

Proper Storage Materials

To avoid PVC damage, always store your coins in holders, flips, and albums made from archival-safe materials:

• Mylar (polyester) flips — these are chemically inert and safe for long-term storage
• Polyethylene or polypropylene holders — these are also safe and widely available
• PCGS, NGC, or ANACS certified slabs — modern slabs use inert plastics specifically designed for coin storage
• Archival-quality albums — look for albums specifically labeled as “PVC-free” and “archival safe”

Never store copper or bronze coins in soft PVC flips, vinyl pages, or cheap plastic containers from unknown manufacturers. The few cents you save on storage materials could cost you hundreds or thousands of dollars in coin value.

Oxidation and Tarnish: The Ever-Present Threat

Oxidation is the most common form of environmental damage affecting copper and bronze coins. Unlike bronze disease, which is a specific chloride-driven corrosion process, oxidation is a broader term that encompasses the various chemical reactions between copper and oxygen, sulfur, and other atmospheric compounds.

Types of Oxidation on Copper and Bronze Coins

In my conservation work, I categorize oxidation on copper and bronze coins into several distinct types:

• Cuprite (red oxide): A thin layer of cuprous oxide (Cu₂O) that forms as a reddish or pinkish film on the coin’s surface. This is the first stage of oxidation and is often seen on freshly minted copper coins that have been exposed to air. In mild form, it can contribute to the attractive “copper glow” that collectors prize. In heavier form, it appears as a dull red or brown coating.
• Tenorite (black oxide): Cupric oxide (CuO) forms a dark brown to black layer on the coin’s surface. This is commonly seen on older copper coins and can be quite stable and protective. Many collectors prefer a coin with a natural tenorite patina to a bright, freshly cleaned piece.
• Malachite (green carbonate): Copper carbonate (Cu₂(CO₃)(OH)₂) forms the familiar green patina seen on aged bronze and copper. When formed slowly under stable conditions, malachite patina is protective and aesthetically pleasing. When formed rapidly or in the presence of chlorides, it can be associated with bronze disease.
• Sulfide tarnish: Exposure to sulfur compounds (from rubber bands, wool, certain papers, or polluted air) produces copper sulfide, which appears as a dark brown or black film. This is the numismatic equivalent of silver tarnish and can often be reduced or removed with proper conservation techniques.

When Oxidation Becomes a Problem

A light, even patina on a copper or bronze coin is generally desirable and should not be removed. In fact, removing a natural patina will almost always reduce a coin’s grade and value. However, oxidation becomes a problem when:

• It is uneven, obscuring design details or mint marks
• It is actively progressing (the coin’s appearance is changing noticeably over time)
• It is associated with chloride contamination (potential bronze disease)
• It is so heavy that it obscures the coin’s original luster and surface characteristics
• It has been accelerated by improper cleaning or environmental exposure

Proper Chemical Conservation: The Acetone Dip and Beyond

When environmental damage has already occurred, proper chemical conservation can often stabilize or improve a coin’s condition. However, I cannot stress this enough: chemical conservation should be approached with extreme caution, and valuable coins should always be treated by a professional.

The Acetone Dip: What It Does and What It Doesn’t Do

The acetone dip is one of the most widely discussed — and most widely misunderstood — conservation techniques in numismatics. Here is what every collector needs to know:

Acetone (CH₃COCH₃) is a powerful organic solvent that is excellent at dissolving organic contaminants from coin surfaces. It will remove:

• PVC plasticizer residue and haze
• Adhesive residue from stickers, tape, or labels
• Oils and greases from handling
• Some types of lacquer or varnish (though not all)
• Organic grime and dirt

Acetone will NOT:

• Remove natural patina or toning
• Remove corrosion products (rust, verdigris, etc.)
• Improve the grade of a worn coin
• Reverse etching or pitting caused by PVC damage
• Change the color of a coin that has been artificially treated

This last point is critical. Many collectors believe that an acetone dip will reveal the “true” color of a coin that has been artificially toned or dipped. In fact, acetone is non-reactive with copper and copper alloys under normal conditions. It will not strip toning or patina. If a coin’s color changes after an acetone soak, it is because the acetone dissolved a thin layer of lacquer or other coating that was masking the true surface — not because it removed the toning itself.

How to Perform an Acetone Dip

If you choose to perform an acetone dip on a common, low-value coin (and I want to emphasize that you should practice on common coins before attempting this on anything of value), here is the proper procedure:

1. Use pure, reagent-grade acetone. Do not use nail polish remover, which contains oils, fragrances, and other additives that can leave a residue on the coin’s surface. Purchase pure acetone from a chemical supply company or hardware store.
2. Work in a well-ventilated area. Acetone is highly flammable and its vapors are harmful. Do not use acetone near open flames, and ensure adequate ventilation.
3. Place the coin in a glass or ceramic container. Do not use plastic containers, as acetone will dissolve many plastics.
4. Cover the coin completely with acetone. Allow it to soak for 5–15 minutes. For heavy PVC contamination, you may need to soak the coin for several hours or repeat the process multiple times with fresh acetone.
5. Remove the coin and allow it to air-dry. Do NOT rinse the coin with water. Do NOT rub or wipe the coin. Allow the acetone to evaporate naturally. The evaporation process is rapid — usually less than a minute.
6. Inspect the coin under magnification. If PVC residue remains, repeat the process. If the coin is clean, store it immediately in an archival-quality holder.

When NOT to Use Acetone

Do not use acetone on:

• Coins with active bronze disease (acetone will not address the chloride contamination and may accelerate the corrosion by removing protective surface layers)
• Coins with artificial toning that you wish to preserve (while acetone won’t remove the toning itself, it may destabilize it)
• Coins in certified slabs (obviously — you cannot dip a coin without removing it from the holder)
• Coins with porous or unstable surfaces (the acetone may penetrate cracks and crevices, causing internal damage)

Prevention: The Best Conservation Is No Conservation

In my years of conservation work, I have come to believe that the single most important thing a collector can do is prevent environmental damage before it occurs. Conservation treatments, no matter how skilled, always involve some degree of risk. A coin that has never been damaged is always more valuable — both monetarily and historically — than a coin that has been treated.

Environmental Controls

Here are the environmental factors you should control to protect your copper and bronze coins:

• Humidity: Maintain relative humidity between 30% and 45%. Above 50%, the risk of bronze disease and accelerated oxidation increases dramatically. Above 70%, active corrosion can begin within days. Use silica gel packets, dehumidifiers, or climate-controlled storage for valuable collections.
• Temperature: Store coins in a cool, stable environment. Avoid attics, garages, and other locations with wide temperature fluctuations. Temperature changes cause condensation, which provides the moisture needed for corrosion reactions.
• Air quality: Avoid storing coins near sources of sulfur (rubber, wool, certain papers), chlorine (bleach, cleaning products), or acidic vapors (wood finishes, adhesives). If you live in an area with high air pollution, consider sealed storage with activated charcoal filters.
• Light: While light does not directly corrode copper or bronze, prolonged exposure to UV light can degrade plastic holders and accelerate the breakdown of protective coatings. Store coins in a dark environment.

Handling Best Practices

How you handle your coins matters just as much as how you store them:

• Always handle coins by the edges, never by the faces
• Wear clean cotton gloves when handling valuable or high-grade copper coins
• Never clean a coin with commercial cleaners, abrasives, or metal polishes
• Do not store coins in direct contact with paper, cardboard, or wood (these materials can off-gas acids and sulfur compounds)
• Inspect your collection regularly — at least quarterly — for signs of environmental damage

The PCGS Registry Dilemma: A Conservator’s Perspective

Returning to the forum discussion that inspired this article, I want to offer a conservator’s perspective on the PCGS Registry situation. The collector’s frustration is understandable: the discontinuation of in-slab TrueView photography forces a choice between preserving the numismatic value of a legacy holder and obtaining high-quality digital images for the Registry.

From a conservation standpoint, however, I would gently suggest that the collector consider the long-term health of the coins themselves. If a coin has been sitting in a Rattler or OGH for 30+ years, it may benefit from being examined, conserved if necessary, and placed in a modern, chemically inert holder. The numismatic premium for a legacy holder is real, but it is meaningless if the coin inside has been damaged by decades of suboptimal storage conditions.

The forum poster mentioned that half of the coins submitted were in OGHs and Rattlers, and the other half were mostly CAC-stickered. For the CAC-stickered coins, the calculus is different — removing the coin from the holder means losing the CAC sticker and the associated premium, plus the cost of re-stickering. In these cases, I would recommend uploading your own high-quality photographs to the Registry (as several forum members noted, this is still possible) and leaving the coins in their current holders. Invest in a good macro lens and a lightbox — the results can rival professional photography, and you maintain the integrity of the holder and sticker.

For the coins in Rattlers and OGHs, I would encourage the collector to carefully evaluate each coin’s condition before deciding whether to reholder. If the coin shows any signs of environmental damage — PVC haze, bronze disease, or active corrosion — reholder it immediately, regardless of the holder premium. A coin in perfect condition in a modern holder is worth far more than a damaged coin in a Rattler.

Actionable Takeaways for Buyers and Sellers

Whether you are buying, selling, or simply maintaining a collection, here are the key action items from this article:

For Buyers:

• Always inspect copper and bronze coins for signs of bronze disease, PVC damage, and active oxidation before purchasing
• Be wary of coins stored in soft PVC flips — the damage may be irreversible
• Ask sellers about storage conditions and provenance
• Consider the cost of conservation when evaluating the purchase price of a damaged coin
• For certified coins, examine the holder for signs of deterioration — cracked seams, cloudiness, or chemical residue

For Sellers:

• Store your coins in archival-quality, PVC-free holders before listing them for sale
• Disclose any known environmental damage or conservation treatments
• High-resolution, well-lit photographs are essential — they build buyer confidence and reduce the risk of returns
• If you have coins in legacy holders, consider having them professionally photographed before deciding whether to reholder

For All Collectors:

• Invest in proper storage materials — Mylar flips, archival albums, and climate-controlled storage
• Inspect your collection regularly for signs of environmental damage
• Learn to identify bronze disease, PVC damage, and active oxidation
• When in doubt, consult a professional conservator — the cost of consultation is far less than the cost of a ruined coin
• Never attempt chemical conservation on a valuable coin without proper training and equipment

Conclusion: Protecting Our Numismatic Heritage

The coins in our collections are more than metal discs with monetary value. They are artifacts of human history — tangible connections to the civilizations, economies, and artisans that produced them. A Roman bronze sestertius connects us to the streets of ancient Rome. A U.S. large cent connects us to the founding of a nation. A beautifully patinated Indian Head cent connects us to the American frontier.

Environmental damage — whether from bronze disease, PVC plasticizer, oxidation, or improper storage — threatens these connections. Every coin lost to corrosion is a piece of history that can never be recovered. As collectors, we are stewards of these artifacts, and it is our responsibility to protect them.

The PCGS forum discussion about TrueView photography and legacy holders may seem like a minor administrative issue, but it highlights a much larger truth: the way we store and care for our coins has a direct impact on their long-term survival. Whether you choose to keep your coins in their original Rattlers, reholder them in modern slabs, or upload your own photographs to the Registry, the most important thing is that you are thinking about the long-term health of your collection.

Improper storage is the enemy of numismatics. But with knowledge, vigilance, and the right materials, we can ensure that our coins — and the history they represent — survive for generations to come.

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