Verdigris and PVC: Saving Possible 1964 SMS Lincoln Cent from Environmental Damage

Improper Storage Is the Enemy of Numismatics

I’ve handled thousands of bronze coins over the years, and if there’s one thing I’ve learned, it’s this: improper storage is the silent assassin of our hobby. When a collector reaches out about a “possible 1964 SMS Lincoln Cent”—a coin that carries the allure of one of the most controversial and rare modern U.S. issues—the first thing I assess isn’t the die polish marks or rim characteristics. It’s the state of environmental degradation. Because if the preservation is compromised, the provenance becomes irrelevant, and all that collectibility slips away.

Let’s talk about what environmental damage looks like on a bronze coin. Because a 1964 Lincoln cent, whether a genuine SMS specimen or a business strike, is a bronze alloy that demands specific conservation protocols. Ignoring those protocols means watching your coin’s eye appeal—and its numismatic value—erode over time.

Understanding the 1964 Lincoln Cent: Composition and Vulnerability

The 1964 Lincoln cent is composed of 95% copper, with the remaining 5% divided between tin and zinc—a classic bronze alloy that has been the standard for U.S. cents since 1909. That composition gives the coin its distinctive warm reddish-gold color, and it’s exactly what makes it uniquely susceptible to a specific set of environmental threats.

Unlike later clad coins (post-1982), which feature a copper-plated zinc core, the solid bronze construction of the 1964 cent reacts to its environment in ways that can either enhance or destroy its value. In my experience grading and conserving 1964 cents, I’ve seen everything from beautifully preserved specimens with stable, vibrant patina to coins so degraded by environmental neglect that their numismatic value has been reduced to zero.

The 1964 SMS Lincoln Cent—if it exists in the manner some collectors hope—is particularly vulnerable because of its experimental nature and the tiny number of known examples. Only 24 have been professionally graded by PCGS, with none graded by NGC or CAC, making each specimen irreplaceable. When environmental damage strikes such a coin, the loss is permanent and immeasurable. There is no mint condition left to salvage once the surface integrity is gone.

What Is Bronze Disease?

Bronze disease is the bane of every copper-alloy coin collector—and I mean every single one of us. It is an active, cyclical corrosion process caused by chloride compounds, typically from handling with bare hands, storage in humid environments, or contact with certain plastics. These compounds attack the copper molecules in the alloy and set up a self-perpetuating cycle of destruction.

I’ve watched bronze disease destroy coins that were otherwise pristine. The process begins microscopically: chloride ions penetrate the surface patina and react with the copper to form cuprous chloride (CuCl). That compound then reacts with moisture and oxygen to form cupric chloride (CuCl₂), which in turn attracts more chloride ions. The cycle feeds itself.

The damage manifests in ways you can actually see:

• Small, raised spots or pustules on the coin’s surface
• A powdery, light-green or brownish residue that cannot be wiped away without damaging the underlying metal
• Pitting and cratering in advanced stages
• Active “weeping” of chloride crystals visible under magnification

For a 1964 Lincoln cent, this is especially insidious. The coin’s value depends heavily on its surface integrity. Any pitting or corrosion on a coin that might command five-figure prices destroys the very surfaces that graders evaluate for strike quality and luster. Once those fields are damaged, the rare variety’s collectibility plummets.

PVC Plasticizer Damage: The Whitman Folder Trap

One of the most common forms of environmental damage I encounter—and one that was unfortunately on full display in the forum discussion surrounding the “possible 1964 SMS Lincoln Cent”—is PVC plasticizer damage. Many coin holders, flips, and albums manufactured before the mid-1980s contain polyvinyl chloride (PVC), which off-gasses plasticizers over time. Those plasticizers migrate onto the coin’s surface and bond chemically with the metal.

In my experience, PVC damage on a 1964 Lincoln cent presents as:

1. Cloudy, hazy patches that appear milky or iridescent under magnification
2. Sticky or tacky surface residue that attracts dust and debris
3. Irreversible etching where the PVC has chemically reacted with the copper surface, creating microscopic grooves
4. Discoloration halos around areas of prolonged contact, often appearing as yellowish or brownish shadows

The forum discussion revealed a collector who had housed their coin in a Whitman folder—a common entry-level storage method that, unfortunately, often contains PVC-based plastics. While Whitman folders are acceptable for short-term storage of common-date coins (and the forum responders were quick to note that a business-strike 1964 cent belongs in a Whitman folder), long-term storage of any bronze coin in PVC-containing materials is a conservation disaster waiting to happen.

Here’s my advice: if you store coins in older flips or albums, replace them with archival-quality, PVC-free materials immediately. Look for flips labeled “polypropylene” or “Mylar” and storage holders certified by PCGS or NGC. Your coin’s eye appeal and long-term numismatic value depend on it.

Oxidation and Toning: Friend or Foe?

One of the most debated topics in the forum discussion was the nature of the toning and tarnish streaks visible on the coin in question. Toning on bronze coins is a complex subject, and as a conservator, I can tell you that not all toning is created equal—or is harmful.

Natural, stable toning occurs when a bronze coin is exposed to atmospheric oxygen over extended periods. The copper in the alloy reacts to form a thin layer of copper oxide and subsequently copper carbonate, creating a protective barrier that preserves the underlying metal. On a 1964 Lincoln cent, natural toning can appear as:

• Warm, iridescent blues, purples, and golds that follow the coin’s contour
• Even, graduated color shifts from the original red copper to darker brown or chocolate tones
• A smooth, unbroken surface texture under magnification

That kind of toning actually enhances eye appeal and can boost numismatic value—provided it’s stable and not actively eating into the metal.

Artificial or environmentally damaging toning, on the other hand, is a different beast entirely:

• Harsh, angular streaks that follow the direction of environmental exposure (e.g., along the edges where moisture entered a holder)
• Dark, mottled brown or black spots that lack the iridescent quality of natural toning
• Surface texture that appears etched, granular, or pitted under 10x magnification

In the forum discussion, the matching toning spots and tarnish streaks between the photos in question were a significant red flag. When I see identical toning patterns across multiple images of the same coin taken under different lighting conditions, I know that either the coin has been artificially toned or the photos are of different coins entirely. For a 1964 SMS Lincoln Cent—where authentication is already a minefield—any sign of artificial enhancement immediately disqualifies the coin from serious consideration.

Proper Chemical Conservation: The Acetone Dip Protocol

When I encounter a bronze coin with PVC damage or surface contamination, one of the most effective conservation techniques I employ is the acetone dip. This process, when performed correctly, removes surface PVC residue and artificial toning without harming the underlying metal. It’s a delicate procedure, and I’ve refined my approach over years of working with copper-alloy coins.

Here is the protocol I follow for conserving a 1964 Lincoln cent or any bronze coin:

1. Assessment: Examine the coin under 10x magnification to identify all surface anomalies. Photograph the coin in raking light to document the current condition before any intervention.
2. Material selection: Use only pure acetone (100% acetone, not nail polish remover, which contains oils and other additives). Acetone is the solvent of choice because it dissolves PVC plasticizers without reacting with copper or bronze alloys.
3. Procedure: Using a pair of soft, lint-free cotton gloves, hold the coin with tongs or a soft grip. Apply a small amount of acetone to a soft, white cotton cloth or a dedicated cotton swab. Gently dab (never rub) the affected areas of the coin’s surface. The PVC residue will dissolve and transfer to the cloth.
4. Rinsing: After the dip, rinse the coin in distilled water to remove any acetone residue. Distilled water is critical—tap water contains minerals and chlorine that can cause new corrosion.
5. Drying: Allow the coin to air-dry completely on a clean, soft surface. Do not blow-dry or use heat.
6. Post-conservation storage: Place the coin in a PVC-free holder, such as an archival-quality flip or a coin capsule, and store it in a cool, dry environment with stable humidity (ideally 40-50% relative humidity).

Important caveat: Acetone dipping should never be performed on coins with active bronze disease. If chloride compounds are present and active, acetone will not stop the corrosion—it will merely remove the surface PVC, leaving the disease to continue unchecked. In cases of active bronze disease, the coin requires a more specialized conservation treatment involving benzotriazole (BTA) solution, which I can only recommend performing under the guidance of a professional conservator.

A word of caution to collectors: never attempt to “clean” a potentially valuable coin with household chemicals, abrasive materials, or ultrasonic cleaners. The surface of a bronze coin is its history. Any intervention that removes original surfaces destroys numismatic value and erases the very luster and patina that make the coin worth preserving.

Environmental Damage vs. Authenticity Markers: What to Look For

One of the trickiest aspects of evaluating a possible 1964 SMS Lincoln Cent is distinguishing between environmental damage and genuine authentication markers. The forum discussion was rife with references to die polish marks, rim characteristics, and strike quality—and for good reason. Genuine SMS coins from the 1965-1967 issues (and the disputed 1964 specimens) possess specific characteristics that differ from business-strike coins:

• Die polish marks: SMS coins were struck from dies that received additional polishing to achieve a proof-like finish. These marks appear as parallel lines or “flow lines” in the fields of the coin, visible under magnification.
• Rim characteristics: The rim of an SMS coin typically displays sharper, more defined lettering and a squared-off profile compared to the softer, more rounded rim of a business strike.
• Strike quality: SMS coins exhibit full, deep strikes with minimal soft spots, particularly in the hair details of Lincoln’s profile and the wheat stalks on the reverse.
• Surface reflectivity: The field surfaces of genuine SMS coins have a distinctive semi-matte to proof-like reflectivity that differs from the cartwheel luster of a business strike.

But here’s the catch: environmental damage can mimic or obscure these features. Bronze disease pustules can be mistaken for die polish marks. PVC damage can create a hazy surface that mimics the semi-matte appearance of an SMS strike. Oxidation can darken the fields to the point where die polish lines become invisible. As a conservator, my first job is always to stabilize the coin’s condition before any authentication discussion can proceed. You can’t evaluate the numismatic value of a coin whose surfaces are actively deteriorating.

The Provenance Problem and the Conservation Reality

One aspect of the 1964 SMS Lincoln Cent that the forum discussion highlighted is the provenance issue. All known genuine 1964 SMS examples trace their lineage to the estate of former Mint Director Eva Adams, who oversaw the Mint in the 1960s. Unless a collector can demonstrate a direct connection to this provenance, the probability of possessing a genuine 1964 SMS cent approaches zero.

But even if provenance were not an issue, the conservation reality remains: any environmental damage to a 1964 Lincoln cent—regardless of its status as SMS or business strike—must be addressed with the utmost care. A coin that has been stored improperly for 70-plus years, as the forum poster claimed, has had decades for PVC migration, oxidation, and potential chloride exposure to do their work. By the time a collector discovers the damage, the mint condition is often already compromised beyond easy repair.

In my professional opinion, the first step for any collector who believes they possess a 1964 SMS Lincoln Cent is not to argue about die polish marks or rim characteristics on internet forums. It is to:

1. Have the coin professionally conserved by a reputable numismatic conservator
2. Submit the coin to PCGS or NGC for authentication and grading
3. Document the coin’s provenance with as much evidence as possible
4. Accept that the odds of a 1964 SMS cent appearing in a private collection without direct Mint connection are vanishingly small

Conclusion: Preserving History Through Proper Conservation

The 1964 Lincoln cent occupies a unique place in American numismatics. Whether it is a genuine SMS specimen—one of the rarest and most debated modern U.S. coins—or a common business strike found in circulation, it represents a pivotal moment in the history of U.S. coinage. The coin’s bronze composition, its historical context, and its potential value (genuine SMS examples command five-figure prices) make it a coin that demands the highest standards of care and conservation.

As a numismatic conservator, my message to collectors is simple: the environment is always working against your coins. Bronze disease, PVC plasticizer damage, and oxidation are relentless processes that will degrade any copper-alloy coin given enough time and improper storage. But these processes are also preventable—and in many cases, reversible—if addressed correctly and promptly.

Whether you are a seasoned collector evaluating a possible 1964 SMS Lincoln Cent or a beginner filling your first Whitman folder, I urge you to prioritize preservation. Use archival-quality storage materials, maintain stable environmental conditions, and consult a professional conservator before attempting any chemical treatments. The coins in our collections are not just metal—they are tangible links to history, and they deserve to be preserved for future generations.

The most valuable coin is not the rarest or the most expensive. It is the one that has been cared for properly, with knowledge, patience, and respect for the material science that makes numismatics possible. That is the conservator’s creed, and it applies to every copper cent we hold in our hands.

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