Verdigris and PVC: Saving a 1918 Illinois Lincoln Commemorative Half Dollar from Environmental Damage

There’s a quiet tragedy playing out in coin cabinets across the country, and most collectors don’t even realize it’s happening. I’m talking about environmental damage — the slow, invisible destruction of some of the most beautiful pieces in American numismatics. And few coins illustrate this threat better than the 1918 Illinois Lincoln Centennial Commemorative half dollar.

A while back, images of one particular example crossed my desk, and I haven’t been able to stop thinking about it. This wasn’t just any Illinois half. We’re talking about a coin that forum members estimated at MS-64 to MS-67, with the owner noting it was already holdered at ANACS MS-66 — possibly with a CAC sticker. The kind of coin where someone described the cartwheel luster as “off the charts,” blazing bright even beneath a layer of tarnish. A coin with genuine numismatic value and eye appeal to match.

But here’s what kept me up at night: that tarnish, the “soapbox” holder it was stored in, and the very real environmental threats that could be quietly eating away at this coin’s surface — and its value — as we speak.

Understanding the 1918 Illinois Lincoln Commemorative Half Dollar

Before we talk about what can go wrong, let’s talk about what makes this coin worth protecting. The 1918 Illinois Centennial half dollar was struck to commemorate the 100th anniversary of Illinois statehood. John R. Sinnock — who would later design the Roosevelt dime — created the obverse featuring Abraham Lincoln’s portrait, while the reverse showcases an eagle perched on a rock before a rising sun, adapted from George T. Morgan’s work. It’s a coin that holds a distinctive place in the commemorative series, both historically and aesthetically.

Key Specifications

• Composition: 90% silver, 10% copper
• Diameter: 30.6 mm
• Weight: 12.5 grams
• Mint: Philadelphia (no mint mark)
• Mintage: 100,058 pieces
• Designer: John R. Sinnock (obverse), George T. Morgan (reverse, adapted)

That 90% silver, 10% copper composition is the key to everything we’re about to discuss. While people tend to think of silver as relatively stable, that copper content introduces real chemical vulnerabilities. The silver has its own set of enemies, too. Understanding the metal is the first step to understanding the threat.

The Silent Killer: Oxidation and Tarnish on Silver Alloy Coins

The original poster made an observation that told me a great deal: the “cartwheel mint luster is so bright under the tarnish.” That single sentence is numismatic gold — it means the underlying surface quality is exceptional, and the damage, so far, is superficial.

What Is Tarnish, Really?

Tarnish on a 90/10 silver-copper alloy is primarily silver sulfide (Ag₂S) — a chemical compound that forms when the coin encounters sulfur-bearing molecules in the air. And those molecules are everywhere:

• Cardboard and paper storage materials (especially older, non-archival stock)
• Rubber bands and elastic materials
• Certain types of wood — oak, in particular, off-gasses sulfur compounds relentlessly
• Adhesives used in coin albums and flips
• Air pollution, especially in urban or industrial settings

The copper in the alloy adds another layer of risk. Copper reacts with oxygen and moisture to form cuprous oxide (Cu₂O) and eventually cupric oxide (CuO), which shows up as darkening or mottling across the surface. In coins with higher copper content, this deterioration can closely mirror what conservators call “bronze disease.” And that’s where things turn serious in a hurry.

Why Tarnish Matters for Grading

Here’s something that catches many collectors off guard: active tarnish is not a stable condition. It’s an ongoing chemical reaction. A coin displaying attractive, original toning — the “rainbow” or “cabinet” toning we all love — can actually see its grade and market value enhanced. But uncontrolled, patchy, or corrosive tarnish? That will absolutely hurt a grade. Graders at PCGS and NGC evaluate three critical factors:

1. Originality of the surface: Is the toning natural and undisturbed, or has the coin been dipped, cleaned, or artificially enhanced?
2. Evenness of color: Patchy, uneven discoloration suggests environmental exposure and can result in a details grade rather than a numerical one.
3. Presence of active corrosion: Any sign of ongoing chemical deterioration raises an immediate red flag.

For a coin like this Illinois Lincoln being discussed at the MS-66 to MS-67 level, even minor surface issues from oxidation can mean the difference between a $2,000 coin and a $500 coin. I’m not exaggerating — that’s the reality of today’s commemorative market at gem and super-gem levels.

PVC Plasticizer Damage: The Hidden Threat in Your Collection

One forum poster mentioned the coin is stored “in a soapbox.” A soapbox is the original cardboard-and-glassine packaging that many early commemorative halves were sold in. And this is where I need to sound a serious alarm for anyone storing coins in or near these original holders.

What Is PVC Damage?

PVC — polyvinyl chloride — was the standard plastic used in coin flips, folders, and albums from the 1960s well into the 2000s. The problem is that PVC is chemically unstable. Over time, it releases chlorine-based plasticizers — the compounds added to keep the plastic flexible. These plasticizers migrate to the coin’s surface and react with the metal, leaving behind a distinctive greenish, sticky, or waxy film that is extraordinarily difficult to remove without professional intervention.

The progression of PVC damage typically unfolds in three stages:

1. Stage 1 — Early: A faint greenish or cloudy haze appears on the surface. The coin may feel slightly tacky. At this point, the damage is often reversible with prompt treatment.
2. Stage 2 — Moderate: The green film becomes more pronounced, often appearing in streaks or patches that map exactly to where the coin contacted the PVC material. Surface pitting begins to show under magnification.
3. Stage 3 — Advanced: Deep green corrosion products blanket significant portions of the surface. Pitting is visible to the naked eye. Original luster is permanently destroyed. The coin is typically relegated to space-filler or details-graded status.

Soapboxes and PVC: An Indirect but Dangerous Connection

You might wonder what a cardboard soapbox has to do with PVC. The answer is proximity and storage context. Many collectors who purchased Illinois halves in original soapboxes also stored them alongside other coins in PVC flips or albums. The sulfur compounds from the soapbox cardboard can interact with PVC off-gassing, creating a particularly aggressive chemical environment. Even if the soapbox itself contains no PVC, the glassine envelope inside can trap moisture and chemical residues directly against the coin’s surface, accelerating both tarnish and corrosion.

My strong recommendation: If you own a 1918 Illinois Lincoln half in its original soapbox, remove the coin now. Place it in an archival-quality, PVC-free holder — a Mylar flip, a PCGS/NGC slab, or at minimum, a non-PVC polypropylene flip. The soapbox itself has collectible value and provenance significance, so store it separately and preserve it.

Bronze Disease: A Threat Even to Silver Alloys

You might assume “bronze disease” only affects ancient bronze coins or modern copper pieces. I wish that were true. The 10% copper content in the Illinois half dollar’s alloy makes it vulnerable to a related form of chloride-induced corrosion that operates through essentially the same mechanism.

The Chemistry of Bronze Disease

Bronze disease is triggered by the presence of chloride ions on or within a copper-alloy surface. These chlorides can come from surprisingly common sources:

• Handling the coin with bare hands — the salt on your skin is enough
• Exposure to salt air in coastal environments
• Contact with chlorinated cleaning products
• Burial in soil, for excavated specimens
• Storage in environments with high humidity and salt content

Once chloride ions are present, they react with copper in the presence of moisture and oxygen to form cuprous chloride (CuCl). This compound then reacts further to produce basic copper chloride (Cu₂(OH)₃Cl), which appears as bright green, powdery spots on the surface. The reaction is self-sustaining and autocatalytic — once it starts, it feeds on itself and will continue spreading unless the chloride source is eliminated.

Identifying Bronze Disease on a 1918 Illinois Half

On a silver-copper alloy coin like the Illinois Lincoln, bronze disease may present as:

• Small, bright green spots that appear raised above the surrounding surface
• A rough, powdery texture — though I strongly advise against touching the surface to check
• Spreading discoloration that worsens over time, even in seemingly dry storage
• Pitting beneath the green spots, visible under 5x–10x magnification

If you spot any of these signs on your Illinois half — or any silver-copper alloy coin — act immediately. Bronze disease will not stop on its own, and every day it progresses, you are losing original surface and, with it, grade and collectibility.

Proper Chemical Conservation: The Acetone Dip and Beyond

This is the part collectors always want to know about: what can I actually do to save my coin? As a conservator, I need to draw a bright line between conservation — stabilizing and preserving the coin’s current state — and cleaning — altering the coin’s appearance. The former is both ethical and necessary. The latter is destructive and will get your coin body-bagged by every major grading service.

The Acetone Dip: Your First Line of Defense

Acetone (CH₃COCH₃) is the single most useful chemical tool in a numismatic conservator’s kit. Here’s why:

• It’s a powerful organic solvent that dissolves many surface contaminants — oils, greases, PVC residue, adhesive residue, and organic films — without reacting with the metal itself.
• It evaporates completely without leaving any residue behind.
• It does not dissolve or disturb original toning (silver sulfide) or original luster.

Critical note: You must use pure, reagent-grade or USP-grade acetone — never nail polish remover, which contains oils, fragrances, and other additives that will deposit fresh contaminants on your coin’s surface.

How to Perform an Acetone Dip

1. Work in a well-ventilated area. Acetone is highly flammable and its vapors are harmful. No open flames, no pilot lights — just good airflow.
2. Use a glass container. Acetone will dissolve many plastics. A clean glass jar with a glass or metal lid is ideal.
3. Submerge the coin completely in acetone. Don’t stack coins or let them touch each other.
4. Soak for 5–15 minutes. For light PVC residue or surface oils, 5 minutes usually suffices. Heavier contamination may require a longer soak or a repeat with fresh acetone.
5. Remove the coin with plastic or metal tongs — not your fingers. The acetone strips oils from your skin and transfers them right back to the coin. Let it air-dry on a clean, lint-free surface.
6. Do not rinse with water. Water introduces new contaminants and can promote further oxidation. Acetone evaporates cleanly on its own.
7. Inspect under magnification. If PVC residue or contamination remains, repeat the process with fresh acetone.

What Acetone Cannot Do

I want to be straightforward about the limitations:

• Acetone will NOT remove tarnish (silver sulfide). Tarnish is a chemical compound bonded to the metal surface. Removing it requires either chemical stripping (which destroys originality) or mechanical polishing (which destroys luster). If your Illinois half has attractive, original toning, leave it alone.
• Acetone will NOT stop bronze disease. Bronze disease requires a different treatment approach, typically involving sodium sesquicarbonate or benzotriazole (BTA) stabilization, which I’ll cover below.
• Acetone will NOT restore luster lost to corrosion or cleaning. Once original mint luster is gone, it’s gone forever. No chemical treatment can bring it back.

Treating Bronze Disease: Advanced Conservation

If your 1918 Illinois half shows signs of active bronze disease, an acetone dip alone won’t be enough. Here’s the conservation protocol I recommend:

1. Mechanical removal of visible corrosion products: Under magnification, use a wooden toothpick or fine bamboo skewer to gently remove the powdery green spots. Never use metal tools — they’ll scratch the surface. The goal is to remove the bulk of the copper chloride deposits without disturbing the underlying metal.
2. Sodium sesquicarbonate soak: Prepare a solution of sodium sesquicarbonate (available from conservation supply companies) in distilled water. Submerge the coin for several hours to several days, changing the solution as it discolors. This converts the destructive copper chloride compounds into less harmful forms.
3. Benzotriazole (BTA) treatment: After the sesquicarbonate soak, a brief immersion in a BTA solution (1–3% in ethanol) creates a protective molecular layer on the copper-alloy surface that inhibits future chloride attack. This is a standard museum conservation technique.
4. Thorough drying and stabilization: After treatment, the coin must be dried completely and stored in a stable, low-humidity environment — ideally below 40% relative humidity.

A word of caution: Bronze disease treatment is not a casual weekend project. If you suspect your Illinois half has active bronze disease and the coin is valued at MS-65 or above, consult a professional numismatic conservator. The cost of professional treatment ($50–$200) is trivial compared to the value you stand to lose from a well-meaning but botched attempt.

Preventive Storage: Protecting Your Investment for the Long Term

The best conservation is prevention. Once you’ve addressed any existing environmental damage, you need to make sure it never happens again. Here are my non-negotiable storage recommendations for high-grade commemorative halves like the 1918 Illinois Lincoln:

The Ideal Storage Environment

• Relative humidity: Keep it below 40% RH. Use silica gel packets or a dehumidifier in your storage area. Hygrometers are inexpensive and absolutely essential.
• Temperature: Stable, cool temperatures between 65–72°F. Avoid attics, garages, and basements where temperature and humidity swing wildly.
• Air quality: Keep coins away from kitchens (cooking releases sulfur compounds), bathrooms (humidity), and workshops (chemical fumes).
• Light: Store coins in the dark. Prolonged light exposure, especially UV, accelerates toning and discoloration.

Approved Storage Materials

• PCGS, NGC, or ANACS slabs: The gold standard. These inert, sonically sealed holders provide excellent protection. If your coin is already in an ANACS holder, that’s a solid start — but check that the holder is in good condition with no cracks or signs of chemical off-gassing.
• Mylar (polyester) flips: Inert and safe for long-term storage. Available from suppliers like Lighthouse, Dansco, and Whitman.
• Archival-quality cardboard flips: Must be explicitly labeled “PVC-free” and “archival.” Not all cardboard flips are created equal — always verify the materials.
• Air-tight capsules: Brands like Air-Tite and Capital Plastics produce inert, air-tight hard plastic capsules in various sizes. The 30.6mm size fits half dollars perfectly.

Materials to Avoid

• PVC flips and soft vinyl holders: The single most common cause of preventable damage in coin collections. If it feels soft and flexible and has a strong plastic smell, it probably contains PVC. Get rid of it.
• Rubber bands: Sulfur compounds in rubber will tarnish silver coins rapidly.
• Paper envelopes (non-archival): Standard paper contains sulfur and acids that promote tarnish.
• Wooden cabinets or drawers (unsealed): Wood, especially oak and cedar, off-gasses organic acids and sulfur compounds. If you use wooden storage, make sure it’s sealed with an inert finish and lined with archival material.
• Glassine envelopes (long-term): While glassine is common in original packaging, it’s not truly archival and can trap moisture against the coin’s surface over decades.

Case Study: What This Means for the Forum Coin

Let’s bring this back to the specific coin that sparked this entire discussion. The collector who posted the 1918 Illinois Lincoln described “off the charts” luster with bright cartwheel effects under the tarnish, and noted it was housed in a soapbox. Several experienced graders weighed in with estimates of MS-65 to MS-67, with the coin reportedly already holdered at ANACS MS-66 and possibly carrying a CAC sticker.

Here’s my conservation assessment based on the available information:

1. The tarnish is likely superficial silver sulfide and, if it’s original and undisturbed, may actually be enhancing the coin’s eye appeal. I would not recommend dipping this coin. The toning is part of its character — and part of its grade.
2. The soapbox storage is a genuine concern. I’d recommend removing the coin from the soapbox and verifying that no PVC-containing materials have entered its storage history. If the coin has ever been in a PVC flip, an acetone dip is warranted to remove any plasticizer residue before re-holding.
3. Inspect carefully for bronze disease. At the MS-66 level, even a single spot of active corrosion could become a grading concern. Use a 10x loupe and examine the high points of Lincoln’s cheek, the eagle’s breast, and the fields around the lettering — these are areas where chloride-induced corrosion often takes hold first.
4. If the coin is already CAC-verified at MS-66, it has passed a rigorous quality check. The priority now is preservation, not improvement. Store it properly, handle it minimally, and resist any urge to “improve” it.

Actionable Takeaways for Buyers and Sellers

Whether you’re buying, selling, or simply holding a 1918 Illinois Lincoln commemorative half dollar — or any high-grade silver commemorative — here are the key action items:

For Buyers

• Always inspect under magnification before purchasing. Look for PVC residue (greenish film), bronze disease (bright green powdery spots), and signs of improper cleaning (hairlines, unnatural brightness, dull “dipped” appearance).
• Ask about storage history. Has the coin been in a PVC flip? Has it been dipped? Stored in a soapbox or original holder? The answers reveal a great deal about potential hidden damage.
• Prefer slabbed coins from PCGS, NGC, or ANACS for high-value purchases. While no grading service is infallible, a slabbed coin has been examined by professionals and is protected by an inert holder.
• Consider CAC verification as an additional quality assurance layer, especially in the MS-65 to MS-67 range where small differences in quality translate to large differences in value.

For Sellers

• Do NOT clean your coin before selling. A properly conserved coin is one thing; a cleaned coin is another entirely. Graders can detect cleaning, and a “cleaned” designation will destroy value far more than original tarnish or toning ever would.
• If PVC damage is present, a professional acetone dip may improve the coin’s appearance and grade potential. But be transparent about any conservation work performed.
• Invest in proper storage before sending to a grading service. A coin that arrives at PCGS or NGC in a PVC flip may be flagged for environmental damage, which can directly affect the grade.

For All Collectors

• Audit your collection for PVC. Go through every flip, album, and holder. If it’s not explicitly labeled PVC-free, replace it. This single step will do more to protect your collection’s numismatic value than any other action you can take.
• Monitor humidity. A $10 hygrometer in your storage area can save you thousands in prevented damage.
• Handle coins by the edges only, and consider wearing cotton or nitrile gloves when examining high-grade pieces.

Conclusion: Preserving History, One Coin at a Time

The 1918 Illinois Lincoln Centennial Commemorative half dollar is more than just a coin. It’s a piece of American history — struck to honor both the centennial of Illinois statehood and the legacy of Abraham Lincoln, the man who called Illinois home. With a mintage of just over 100,000 pieces, it’s not a rare variety in absolute terms, but high-grade examples in MS-65 and above are genuinely scarce, and coins at the MS-66 and MS-67 level are condition rarities that command significant premiums.

The environmental threats we’ve discussed — oxidation, PVC damage, and chloride-induced corrosion — are not theoretical risks. They are active, ongoing processes that destroy numismatic value every single day in collections around the world. The good news is that they are also entirely preventable with proper storage, careful handling, and, when necessary, professional conservation.

If you’re fortunate enough to own a gem-quality Illinois Lincoln half like the one discussed in this forum thread, you have a responsibility to preserve it — not just for your own investment, but for the collectors and historians who will come after you. Store it properly. Monitor it regularly. And when in doubt, consult a professional conservator.

That cartwheel luster has survived for over a century. Let’s make sure it survives for a hundred more.

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