Verdigris and PVC Damage: Saving Your Shell Oil State Tokens from Environmental Decay

Improper storage is the silent enemy of numismatics — and it’s probably happening to your collection right now. Let me walk you through the specific signs of environmental damage that target copper-alloy tokens, and what you can do before it’s too late.

As someone who has spent over two decades handling base-metal issues — from ancient Roman bronzes to modern commemorative tokens — I can tell you that the single most overlooked threat to a collection isn’t theft, mishandling, or even market fluctuations. It’s the slow, insidious creep of environmental damage. And few categories of numismatic material illustrate this better than the humble base-metal token, particularly the beloved Shell Oil State Token series issued throughout the late 1960s and 1970s.

When a collector recently posted blurry photographs of a 1969 Shell Oil Texas State Token on a popular forum — asking the perennial question, “What is this? And is it collectible?” — the responses ranged from helpful identification to good-natured ribbing about photo quality. But beneath the surface of that thread lies a far more important conversation that every collector of base-metal numismatic items needs to have: What is environmental damage doing to your tokens right now, and what can you do about it?

In this article, I’ll walk you through the specific environmental threats facing copper, bronze, and brass tokens like the Shell Oil series, how to identify damage in its earliest stages, and — most importantly — what conservation steps you can take to preserve these pieces for future generations.

Understanding the Shell Oil State Token Series: Why These Pieces Matter

Before we get into conservation, let’s establish what we’re protecting. The Shell Oil State Token series was issued beginning in 1969 as a promotional campaign, featuring all 50 United States. These tokens were typically struck in bronze or brass alloys — copper-based metals that are particularly susceptible to environmental degradation. Each token celebrated a different state, making them popular with collectors of Texaniana, Americana, and exonumia.

According to Numista (catalog reference #155180 for the Texas issue), individual tokens in perfect condition tend to sell for under $5 on eBay, while a complete set of all 50 states can fetch around $25. These are not high-value numismatic rarities in the traditional sense, but they hold significant historical and cultural value — and that value is precisely what makes proper conservation worthwhile.

Here’s what every collector of this series should know:

• Metal composition: Primarily copper alloy (bronze/brass), which reacts readily with moisture, chlorides, and acidic compounds.
• Date range: 1969–1970s, meaning these tokens are now 50+ years old and have had decades to accumulate environmental damage.
• Collectibility factors: Completeness of the 50-state set, surface condition, and the absence of active corrosion are the primary drivers of numismatic value.
• Storage history matters: Many of these tokens were originally distributed to the general public and stored in non-archival conditions — cardboard boxes, plastic bags, and yes, PVC flips.

Bronze Disease: The Silent Killer of Copper Alloy Tokens

If there is one term that should strike fear into the heart of every base-metal collector, it is bronze disease. I’ve examined hundreds of copper-alloy tokens and medals over the years, and bronze disease is, without question, the most destructive and most misunderstood form of environmental damage.

What Exactly Is Bronze Disease?

Bronze disease is a form of active corrosion caused by the presence of chlorides (salt compounds) in contact with copper alloys. It manifests as bright green, powdery or crusty spots on the surface of the metal — often mistaken by casual collectors for ordinary patina or verdigris. But unlike stable patina, bronze disease is progressive and self-sustaining. Once it starts, it will continue to eat into the metal until the piece is destroyed.

The chemical process works like this:

1. Chloride ions (from salt, sweat, or environmental exposure) penetrate the copper surface.
2. In the presence of moisture and oxygen, the chlorides react with copper to form cuprous chloride.
3. Cuprous chloride reacts further with moisture and oxygen to produce hydroxychloride compounds — the characteristic bright green spots.
4. This reaction releases hydrochloric acid, which attacks more copper, perpetuating the cycle.

How to Identify Bronze Disease on Your Tokens

In my experience grading and conserving base-metal pieces, here are the telltale signs I look for:

• Bright, almost neon-green spots or crusts — distinctly different from the darker, more uniform green or brown patina that develops naturally over time.
• Powdery or fuzzy texture — stable patina feels smooth to the touch; bronze disease feels gritty or raised.
• Active spreading — if you photograph a spot and revisit the token weeks later, the spot will have grown.
• Pitting beneath the green crust — when carefully examined under magnification, you’ll see that the metal surface underneath the green deposits is being eaten away.

If you spot any of these signs on your Shell Oil tokens — or any copper-alloy numismatic item — do not ignore it. Bronze disease will not stop on its own.

PVC Plasticizer Damage: The Hidden Threat in Your Storage Materials

Here’s a fact that surprises many collectors: the very materials you use to store your tokens may be destroying them. Polyvinyl chloride (PVC) — the soft, flexible plastic used in many coin flips, folders, and storage pages — releases plasticizer chemicals over time. These chemicals react with the metal surface of copper-alloy tokens, causing a distinctive and often irreversible form of damage.

What PVC Damage Looks Like

PVC damage typically presents as:

• A greenish, sticky, or slimy film on the token’s surface — sometimes described as “PVC slime.”
• Haze or cloudiness that cannot be wiped away with a dry cloth.
• Surface etching — in advanced cases, the plasticizer chemicals actually etch into the metal, leaving permanent marks that obscure design details and destroy eye appeal.
• A distinctive chemical odor — if you open a PVC flip and detect a sharp, plasticky smell, that’s the off-gassing that causes the damage.

Why This Matters for Shell Oil Tokens

Many Shell Oil tokens from the 1960s and 1970s were stored by their original recipients in whatever was handy — and PVC flips and bags were among the most common storage solutions of that era. If you’ve acquired tokens that were previously stored in PVC, there’s a significant chance they already carry some degree of plasticizer damage.

My strong recommendation: Remove every copper-alloy token from PVC immediately. Replace PVC flips with Mylar (polyethylene terephthalate) flips, which are chemically inert and will not react with metal surfaces. For long-term storage, consider archival-quality cardboard 2×2 holders or air-tight capsules made of inert plastic.

Oxidation and Patina: Understanding the Difference Between Beautiful and Destructive

Not all surface changes on a copper-alloy token are cause for alarm. In fact, many collectors prize the natural patina that develops on bronze and brass over decades. Understanding the difference between beneficial oxidation and destructive corrosion is one of the most important skills a numismatic conservator can develop.

Stable Patina: The Collector’s Friend

When copper alloys are exposed to clean, dry air over long periods, they develop a thin layer of copper oxide that gradually darkens from reddish-brown to deep chocolate or even near-black. This layer is chemically stable and actually protects the underlying metal from further corrosion. On Shell Oil tokens, a smooth, even brown patina is generally considered desirable and should not be removed. It adds character and provenance without compromising the strike or detail.

Destructive Oxidation: When to Intervene

Problems arise when oxidation is uneven, accelerated, or combined with contaminants. Watch for:

• Rapid darkening or discoloration — especially if it occurs over weeks or months rather than years.
• Mottled or blotchy coloration — suggesting uneven chemical exposure, possibly from fingerprints, cleaning residues, or environmental pollutants.
• White or gray deposits — which may indicate the formation of zinc oxide or zinc carbonate (particularly common in brass alloys, where zinc is selectively leached from the surface in a process called dezincification).

Proper Chemical Conservation: The Acetone Dip and Beyond

When environmental damage has already occurred, what can a collector do? This is where chemical conservation comes in — and where I must begin with an important caveat.

Conservation Disclaimer: Any chemical treatment carries risk. When in doubt, consult a professional numismatic conservator before attempting any cleaning or stabilization procedure. Irreversible damage from improper treatment can reduce a token’s numismatic value far more than the original environmental damage would have.

The Acetone Dip: Your First Line of Defense

For PVC plasticizer damage specifically, the most commonly recommended treatment is a soak in pure acetone. Acetone is an excellent solvent for the organic plasticizer compounds that cause PVC slime, and it does not react with copper or its alloys when used properly.

Here is the procedure I recommend for treating PVC-damaged tokens:

1. Use only pure, reagent-grade acetone — available from hardware stores or chemical suppliers. Do not use nail polish remover, which contains oils, fragrances, and other additives that can leave residues on the metal surface.
2. Place the token in a glass container (acetone will dissolve many plastics) and submerge it completely in acetone.
3. Soak for 15–30 minutes, gently agitating the container periodically. For heavy PVC contamination, you may need to soak longer or repeat the process.
4. Remove the token and allow it to air-dry on a clean, lint-free cloth. Do not rinse with water — acetone evaporates cleanly and completely.
5. Inspect under magnification to determine if all PVC residue has been removed. If green or slimy residue persists, repeat the soak.
6. Do NOT rub, scrub, or polish the token after the acetone treatment. Mechanical cleaning will scratch the surface, destroy luster, and remove any desirable natural patina.

Treating Bronze Disease: Beyond Acetone

Acetone alone will not stop bronze disease, because the chloride compounds are inorganic and insoluble in acetone. Treating active bronze disease requires a more involved approach:

• Mechanical removal: Under magnification, use a wooden pick or fine bamboo skewer to gently remove the powdery green deposits. This is painstaking work, but it’s essential to eliminate the chloride source.
• Sodium sesquicarbonate soak: After mechanical cleaning, soak the token in a 5% solution of sodium sesquicarbonate (available from conservation supply companies) for several days to weeks. This solution converts the remaining cuprous chloride to stable cuprous oxide.
• Benzotriazole (BTA) stabilization: After the sesquicarbonate soak, a final soak in a 1–3% BTA solution in ethanol can provide a protective molecular layer that inhibits future corrosion. BTA is the gold standard in copper-alloy conservation.
• Thorough drying and sealing: After treatment, dry the token completely and store it in an inert, airtight holder with a desiccant packet to control humidity.

What NOT to Do

In my years of conservation work, I’ve seen well-intentioned collectors cause catastrophic damage by using the wrong methods. Here is a list of treatments to absolutely avoid on copper-alloy tokens:

• Never use vinegar, lemon juice, or other acids — these will strip patina and accelerate corrosion.
• Never use commercial metal polishes (e.g., Brasso, Wright’s Silver Cream) — these contain abrasives that scratch the surface and chemical agents that can react with the metal.
• Never use baking soda or abrasive pastes — same problem: surface scratching and chemical contamination.
• Never attempt electrolytic cleaning on numismatic items — while effective for industrial applications, electrolysis removes metal along with corrosion and destroys surface detail.
• Never store tokens in direct contact with wood, rubber, or acidic paper — all of these materials off-gas chemicals that accelerate corrosion.

Preventive Storage: Building an Environment Your Tokens Can Thrive In

The best conservation is prevention. Once you’ve identified and treated any existing environmental damage, the next critical step is ensuring it doesn’t happen again. Here are my recommendations for proper storage of copper-alloy tokens like the Shell Oil State series:

Ideal Storage Conditions

• Relative humidity below 40% — moisture is the primary driver of both bronze disease and accelerated oxidation. Use silica gel desiccant packets in your storage containers.
• Stable temperature — avoid attics, garages, and basements where temperature fluctuations cause condensation. A climate-controlled interior room is ideal.
• Dark storage — prolonged exposure to light, especially UV, can accelerate certain chemical reactions on metal surfaces.
• Inert storage materials only — Mylar flips, archival cardboard holders, acid-free tissue paper, and glass or inert plastic containers.
• Individual compartmentalization — never store tokens loose in a box where they can rub against each other. Surface contact between coins and tokens causes micro-abrasions that become entry points for corrosion.

A Note on Handling

Always handle tokens with clean, dry hands or, better yet, cotton or nitrile gloves. The oils and salts in human skin are a primary source of chloride contamination that leads to bronze disease. Hold tokens by the edges only, and never touch the obverse or reverse surfaces.

Assessing Collectibility After Environmental Damage

Let’s return to the original forum question: “Is it collectible?” For a 1969 Shell Oil Texas State Token, the answer is a qualified yes — but condition is everything when it comes to numismatic value.

Here’s how environmental damage affects the collectibility and market value of these tokens:

• Mint state with original luster and no damage: $3–$8 on the current market, with premium examples (sharp strike, full detail) at the higher end.
• Light, stable patina with no active corrosion: $2–$5. Collectors of Texaniana and Americana often prefer a natural, undisturbed surface with strong eye appeal.
• PVC damage (surface haze or slime): $1–$3. The damage is visible and detracts from eye appeal, even if the underlying metal is intact.
• Active bronze disease: Under $1, and potentially worthless if the corrosion has eaten into the design details. A token with active bronze disease is also a contamination risk to other pieces in your collection.
• Complete 50-state set in excellent condition: $20–$40, with pristine examples occasionally reaching $50 or more from dedicated exonumia collectors.

The key takeaway for buyers and sellers: a well-conserved token is worth significantly more than a damaged one, and the cost of proper storage materials is trivial compared to the numismatic value preserved.

Actionable Takeaways for Collectors

To summarize everything we’ve covered, here is your action checklist for protecting copper-alloy tokens from environmental damage:

1. Audit your collection today. Remove every copper-alloy token from PVC flips, wooden holders, and acidic paper envelopes.
2. Inspect under magnification. Look for bright green spots (bronze disease), green slime (PVC damage), and uneven discoloration (accelerated oxidation).
3. Treat PVC damage with pure acetone soaks. It’s safe, effective, and inexpensive.
4. Address bronze disease immediately. Mechanical removal followed by sodium sesquicarbonate and BTA treatment is the professional standard.
5. Never use acidic or abrasive cleaners. When in doubt, do nothing and consult a professional conservator.
6. Store in inert materials at low humidity. Mylar flips, archival holders, and silica gel desiccants are your best friends.
7. Handle with gloves, by the edges only. Your fingers are the enemy of copper alloys.
8. Document your collection with sharp, well-lit photographs. As the forum discussion demonstrated, clear photos are essential for accurate identification and condition assessment.

Conclusion: Preserving History, One Token at a Time

The 1969 Shell Oil Texas State Token may never command the prices of a rare Morgan dollar or a gold double eagle, but it represents something equally important: a tangible piece of American commercial and cultural history. These tokens were part of a nationwide promotional campaign that touched millions of lives, and each surviving example is a small artifact of mid-20th-century Americana.

As someone who has dedicated years to this work, I believe our responsibility goes beyond assigning grades and estimating values. It is to ensure that these pieces survive — that the Texas token you pull out of a drawer in 2025 can be passed to a grandchild in 2055, still bearing the detail and character that made it worth collecting in the first place.

Environmental damage is not a death sentence for your collection. Bronze disease can be arrested. PVC damage can be cleaned. Oxidation can be managed. But only if you recognize the signs, understand the chemistry, and take action before the damage becomes irreversible.

The next time you encounter a green-spotted token in a PVC flip at a coin show or estate sale, don’t walk past it. Pick it up, examine it closely, and ask yourself: Can this be saved? More often than the casual collector might think, the answer is yes — and the satisfaction of preserving a piece of history is worth far more than the few dollars it might fetch on eBay.

Your tokens have survived 50 years. With proper care, they’ll survive 50 more.

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