Verdigris and PVC: Saving Your Best of the Mint 1916 Standing Liberty Quarter Dollar Gold Coin and Silver Medal Set from Environmental Damage

Improper storage is the silent enemy of any serious numismatic collection. If you own — or are thinking about acquiring — the Best of the Mint 1916 Standing Liberty Quarter Dollar Gold Coin and Silver Medal Set, you need to understand exactly what environmental threats are lurking in your storage setup right now.

As a numismatic conservator who has spent decades handling everything from ancient bronzes to modern U.S. Mint commemorative sets, I can tell you that few things are more heartbreaking than watching a beautifully preserved coin slowly deteriorate because of an avoidable storage mistake. This set — pairing a 24-karat gold Standing Liberty Quarter with a one-ounce silver medal — contains two very different metal types, each with its own unique vulnerabilities. If you own this set, understanding environmental damage and proper conservation isn’t optional. It is essential.

Understanding What You Are Protecting: The Metals at Play

Before we can talk about damage, we need to understand the materials. The gold coin in the Best of the Mint (BOM) set is struck in 24-karat gold, which is essentially pure gold at 99.99% fineness. Pure gold is remarkably inert. It does not tarnish, it does not corrode in normal atmospheric conditions, and it is largely resistant to chemical attack. From a conservation standpoint, the gold Standing Liberty Quarter is the more forgiving half of the set.

The silver medal, however, is an entirely different story. Silver is reactive. It combines readily with sulfur compounds in the atmosphere to form silver sulfide — the dark tarnish you have undoubtedly seen on silver coins, flatware, and jewelry. Silver is also susceptible to chloride attack and can develop surface issues that range from light toning to severe corrosion if exposed to the wrong environment.

Then there is the original 1916 Standing Liberty Quarter itself — a .900 fine silver coin that, for collectors who own the classic version alongside the modern gold reproduction, presents its own conservation challenges. The copper content in sterling silver (10% in the case of the original quarter) makes it particularly vulnerable to a phenomenon I will discuss in detail below: bronze disease.

The key takeaway here is that a single storage solution must serve two masters — gold and silver — and the storage requirements for silver are far more demanding. When in doubt, store for the more reactive metal.

Bronze Disease: The Silent Killer of Copper-Alloy Coins

Let me be direct: bronze disease is the single most destructive form of corrosion that affects copper-alloy coins. While it primarily threatens bronze, copper-nickel, and sterling silver pieces, any collector who owns the full Best of the Mint set alongside original 1916 Standing Liberty Quarters needs to understand it thoroughly.

What Causes Bronze Disease?

Bronze disease is caused by the presence of chlorides — typically from salt (sodium chloride) or hydrochloric acid — in contact with copper or copper alloys. The chloride ions penetrate the surface of the metal and react with copper to form cuprous chloride. When this compound is exposed to moisture and oxygen, it undergoes a cyclical chemical reaction that produces copper(II) chloride and hydrochloric acid. The acid attacks more copper, producing more cuprous chloride, which reacts again with moisture and oxygen. It is a self-sustaining cycle that will continue until the entire coin is consumed if left unchecked.

How to Identify Bronze Disease

In my experience grading and conserving copper-alloy coins, the signs of bronze disease are distinctive once you know what to look for:

• Bright green, powdery spots or patches on the coin’s surface — these are raised above the surface and feel rough to the touch (if you were to handle an ungraded coin)
• A fuzzy or crusty texture that cannot be wiped away gently
• Spreading patterns — the green spots will grow over time if the coin remains in the same environment
• Pitting beneath the green spots — once the corrosion product is removed, you will find the metal surface has been eaten away, leaving irreversible damage to the design details

If you see any of these signs on a silver Standing Liberty Quarter, you are looking at bronze disease driven by the 10% copper content in the coin’s alloy. The original 1916 quarters are particularly vulnerable because of their age — decades of handling, storage in non-archival materials, and exposure to varying environmental conditions increase the likelihood of chloride contamination.

Treating Bronze Disease

Treatment depends on the severity:

1. Mechanical removal: For mild cases, carefully scraping away the green corrosion products under magnification using a wooden or bamboo pick. This is delicate work and should only be attempted by experienced conservators or under professional guidance.
2. Chemical treatment: Soaking the coin in a 5% sodium sesquicarbonate solution to neutralize the chlorides. This process can take days to weeks, with regular solution changes. The goal is to convert the unstable copper chlorides into stable copper compounds.
3. Stabilization with benzotriazole (BTA): After chloride removal, treatment with BTA forms a protective film on the copper surface that inhibits further corrosion. This is a standard conservation practice for bronze and copper-alloy coins.
4. Final rinse and drying: A thorough rinse in distilled water followed by careful drying, then immediate placement in archival-quality storage.

Do not use commercial “cleaning” products, vinegar, lemon juice, or abrasive methods. These will destroy the surface of the coin and obliterate any numismatic value. If you suspect bronze disease on a valuable piece, consult a professional conservator immediately.

PVC Plasticizer Damage: The Hidden Threat from Flips and Holders

While bronze disease is the dramatic villain of copper-alloy coins, PVC (polyvinyl chloride) plasticizer damage is the quiet, insidious threat that affects virtually every metal type — gold, silver, copper, and nickel alike. And it is almost entirely caused by one of the most common storage mistakes in the hobby.

What Is PVC Damage?

Many coin flips, especially inexpensive ones purchased from non-numismatic suppliers, are made from PVC-containing plastic. Over time, PVC degrades and releases plasticizer chemicals — primarily phthalates — as well as hydrochloric acid. These chemicals migrate to the coin’s surface and create a characteristic greenish, sticky, or hazy film that is extremely difficult to remove without damaging the coin.

Identifying PVC Damage

I have examined thousands of coins submitted for grading, and PVC damage is one of the most common environmental issues I encounter. Here is what to look for:

• A greenish or blue-green film or residue on the coin’s surface, often most prominent in the recessed areas of the design
• A sticky or tacky feel when the coin is handled (again, only for raw, ungraded coins)
• Hazy or cloudy appearance that looks like surface fogging, not the sharp, crystalline green of bronze disease
• Progression over time — PVC damage gets worse the longer the coin remains in contact with the offending material. A coin stored in a PVC flip for five years will show significantly more damage than one stored for six months.

For the Best of the Mint set, this is particularly relevant because many collectors store their gold coins and silver medals in whatever flips or holders came with the set, or in generic flips purchased at a local coin shop. If those flips contain PVC, your coins are slowly being damaged.

Acetone Dips: Proper Chemical Conservation for PVC Damage

The good news is that early-stage PVC damage can often be remediated using a technique I have employed countless times in conservation work: the acetone dip.

Here is the proper protocol:

1. Use only pure, reagent-grade or technical-grade acetone. Do not use nail polish remover, which contains oils, fragrances, and other additives that will leave their own residue on the coin.
2. Work in a well-ventilated area. Acetone is highly flammable and its vapors are harmful. No open flames, no sparks, good ventilation.
3. Submerge the coin in a clean glass container of acetone. Do not rub, scrub, or wipe the coin. Simply let the acetone dissolve the PVC residue.
4. Allow the coin to soak for a few minutes, then remove it and allow it to air dry on a clean, lint-free surface. The acetone will evaporate rapidly, leaving no residue.
5. Repeat if necessary. For heavy PVC damage, multiple fresh baths of acetone may be required. Use clean acetone each time.

Critical warning: Acetone will not harm gold, silver, or copper in their metallic forms. However, it will damage any lacquer, coating, or applied color on a coin. It will also damage plastic holders, capsules, and display cases. Never use acetone on a coin that has been artificially toned or treated with any surface coating. And never use acetone on coins still inside their Mint packaging — remove the coin first.

After an acetone dip, the coin should be immediately transferred to PVC-free, archival-quality storage. Acceptable materials include:

• Mylar (polyethylene terephthalate) flips — the standard for archival coin storage
• Acrylic (polymethyl methacrylate) capsules — rigid, clear, and chemically inert
• Archival cardboard holders with Mylar windows — such as the standard 2×2 holders used by PCGS and NGC for their storage boxes

Avoid soft plastic flips of unknown composition, rubber bands, paper envelopes with adhesive, and any material that smells strongly of plastic. If in doubt, assume it contains PVC and do not use it.

Oxidation and Tarnish: Understanding Silver’s Natural Enemies

While gold in the Best of the Mint set is essentially immune to oxidation under normal conditions, the one-ounce silver medal is not so fortunate. Silver’s tendency to tarnish is one of the most well-known properties of the metal, but many collectors do not fully understand the chemistry or the implications for long-term storage and collectibility.

The Chemistry of Silver Tarnish

Silver tarnish is primarily silver sulfide (Ag₂S), formed when silver reacts with hydrogen sulfide (H₂S) or other sulfur-containing compounds in the atmosphere. Sources of atmospheric sulfur include:

• Industrial pollution and vehicle exhaust — higher in urban environments
• Rubber and latex products — rubber bands, latex gloves, rubber gaskets in storage containers
• Wool and other protein-based textiles — wool contains sulfur-bearing amino acids
• Certain papers and cardboards — especially those treated with sulfur-containing sizing agents
• Adhesives and glues — many common adhesives off-gas sulfur compounds
• Eggs and other sulfur-rich organic materials — yes, storing your coins near a kitchen can contribute to tarnish

The rate of tarnishing depends on the concentration of sulfur compounds, humidity, and temperature. Warm, humid conditions accelerate tarnish formation dramatically.

Natural Tarnish vs. Active Corrosion

As a conservator, it is important for me to distinguish between benign toning and active corrosion. Many silver coins develop attractive, iridescent toning over time — a thin, stable layer of silver sulfide that actually protects the underlying metal. This natural patina can significantly enhance eye appeal and is highly prized by collectors. It should never be removed.

Active corrosion, by contrast, is characterized by:

• Dark, uneven, or blotchy discoloration that obscures design details
• Pitting or roughness on the surface
• Spread to previously unaffected areas over time
• White or gray powdery deposits — these may be silver chloride, indicating chloride attack

If your silver medal from the Best of the Mint set shows any of these signs, it needs immediate attention. Remove it from its current storage, assess the environment, and transfer it to archival-quality materials.

Preventing Oxidation on Silver

Prevention is always preferable to treatment. Here are my recommendations for long-term silver storage:

1. Use acid-free, sulfur-free tissue paper as a wrapping material inside capsules or holders. This provides a chemical buffer between the coin and the holder.
2. Store in a cool, dry environment. Ideal conditions are below 50% relative humidity and stable temperatures between 65-70°F (18-21°C). Avoid attics, basements, and garages where temperature and humidity fluctuate wildly.
3. Consider activated charcoal or silver-specific anti-tarnish strips placed inside your storage container. These absorb sulfur compounds before they can reach the coin. Replace them periodically.
4. Avoid airtight containers in humid environments — paradoxically, sealing a coin in an airtight container with high humidity can create a microclimate that accelerates corrosion. Moderate air circulation is preferable to complete sealing unless you are controlling the atmosphere with desiccants.
5. Never store silver directly against wood, felt, or fabric. These materials off-gas organic acids and sulfur compounds that will attack the metal surface and permanently diminish luster.

Environmental Threats Specific to Modern U.S. Mint Packaging

The Best of the Mint sets arrive in U.S. Mint packaging that, while visually appealing, may not be ideal for long-term conservation. This is a topic that generates considerable debate in the collecting community, and as a conservator, I have strong opinions.

The Problem with Mint Packaging

The Mint ships these sets in presentation boxes that typically include:

• Cardboard or paper components — which may contain sulfur-bearing compounds
• Felt or fabric linings — which off-gas organic acids
• Adhesives — which may contain sulfur or acidic compounds
• Plastic inserts or capsules — of varying quality, some of which may contain PVC

In my experience, the single best thing you can do for the long-term preservation of a Best of the Mint set is to remove the coins and medal from the original packaging and store them separately in archival-quality holders. The display boxes can be stored separately for aesthetic purposes and to preserve provenance, but the coins themselves should be in chemically inert environments.

To Grade or Not to Grade: Conservation Implications

Many collectors feel compelled to have their modern gold coins and silver medals certified and encapsulated by grading services like PCGS or NGC. From a conservation standpoint, professional encapsulation is one of the best things you can do for a coin.

PCGS and NGC use PVC-free, inert plastic slabs that provide:

• A physical barrier against handling damage
• A chemically stable environment inside the holder
• Tamper-evident sealing that protects against environmental exposure
• Authentication and grading that establishes the coin’s condition, strike quality, and identity

The downside is cost — the grading fees add up, especially for a multi-piece set. But for a set with a retail value in the range of $1,590 to $1,627.50 for the quarter alone (at recent gold spot prices), the grading cost is a modest investment in long-term protection. A mint condition coin in a certified slab also commands a meaningful premium on the secondary market, which directly impacts both numismatic value and collectibility.

If you choose not to grade, I recommend storing each piece in a hard acrylic capsule (such as those made by Leuchtturm or Capital Plastics) rather than leaving them in the Mint’s original packaging.

Practical Conservation Checklist for the Best of the Mint Set

Let me summarize the actionable steps every owner — or prospective buyer — of the Best of the Mint 1916 Standing Liberty Quarter Dollar Gold Coin and Silver Medal Set should take:

Immediate Actions

1. Inspect all pieces under magnification (at least 5x-10x) for signs of PVC damage, bronze disease, tarnish, or corrosion. Use a bright, angled light source to reveal surface films and haze that might otherwise go unnoticed.
2. If PVC damage is detected, perform an acetone dip as described above. Use pure acetone, work in ventilation, and allow complete drying before re-storage.
3. Remove coins from Mint packaging if you intend to store them long-term. The packaging is for display, not conservation.
4. Transfer to archival-quality holders — Mylar flips, hard acrylic capsules, or professional grading slabs.

Ongoing Storage Best Practices

• Maintain a cool, dry, stable environment — ideally a climate-controlled safe or safe deposit box
• Use anti-tarnish strips in your silver storage containers and replace every 3-6 months
• Never handle coins with bare hands — cotton or nitrile gloves only
• Avoid rubber bands, paper clips, adhesive notes, or any non-archival material in contact with the coins
• Inspect your collection at least twice a year for early signs of environmental damage. Early detection is the key to successful conservation.

What NOT to Do

• Never use commercial coin cleaners — they are abrasive and will destroy the surface and any remaining luster
• Never use vinegar, lemon juice, baking soda, or any home remedy on valuable coins
• Never rub, polish, or buff a coin to remove tarnish — you are removing metal and destroying surface detail, which permanently reduces eye appeal and value
• Never store coins in PVC flips, plastic bags of unknown composition, or non-archival containers
• Never store in areas with high humidity, temperature fluctuations, or exposure to chemical fumes

The Collector’s Perspective: Balancing Passion and Preservation

What strikes me most about the collecting community’s engagement with these sets is the genuine passion behind every acquisition. Collectors pursue all three 2016 gold coins — the dime, quarter, and half — and plan ahead for future releases despite budget constraints. Others connect these modern tributes to formative memories, like the 2014 Kennedy Half Dollar gold coin that sparked their love of the hobby. These emotional connections are what make numismatics more than just an investment — they are what make it a living, breathing pursuit.

But passion without preservation knowledge can be costly. A $1,600 gold coin that develops PVC haze, or a silver medal that tarnishes into an unsightly mess, is not just an aesthetic loss — it is a financial and historical one. The Best of the Mint program is designed to honor iconic American coin designs, and preserving these tributes in the condition they deserve is our responsibility as collectors.

I would also note that market dynamics — the premiums over spot price, the mintage limits, the debate about whether silver medals add value — all underscore the importance of preservation. A coin in pristine mint condition commands a significant premium over one with environmental damage. For modern commemoratives, where large mintages mean that condition and eye appeal are the primary differentiators, proper conservation is the difference between a coin that holds its value and one that becomes a loss.

When to Call a Professional Conservator

Not every conservation task should be attempted at home. I strongly recommend consulting a professional conservator — or at minimum a reputable grading service — in the following situations:

• Bronze disease is confirmed or strongly suspected — improper treatment can accelerate the damage
• Heavy PVC damage that does not respond to acetone dips — the plasticizer may have penetrated the metal surface
• Active corrosion on silver — particularly if pitting is visible beneath the tarnish
• Any coin with significant numismatic value — the risk of DIY conservation outweighs the cost of professional treatment
• Coins you intend to submit for grading — improper cleaning or conservation can result in details grades or “cleaned” designations that dramatically reduce value

Professional conservators have access to tools and chemicals that are not available to the general public, and — more importantly — they have the experience to assess when intervention is necessary and when it is better to leave a coin alone. Sometimes the best conservation decision is to do nothing except improve the storage environment.

Conclusion: Preserving a Tribute to Hermon MacNeil’s Masterpiece

The Best of the Mint 1916 Standing Liberty Quarter Dollar Gold Coin and Silver Medal Set is more than a modern commemorative. It is a tribute to one of the most beautiful coins in American numismatic history — Hermon MacNeil’s Standing Liberty Quarter, first issued in 1916 and immediately hailed as a masterpiece of coin design. The original 1916 quarter, with its legendary low mintage of just 52,000 pieces, is one of the most sought-after key dates of the entire series. The gold reproduction in the BOM set allows collectors to own that iconic design in pure gold, paired with a silver medal that celebrates the same artistic heritage.

As a conservator, I see my role as ensuring that these tributes survive in the best possible condition for future collectors. The threats are real — bronze disease on copper-alloy pieces, PVC damage from improper storage, oxidation on silver — but they are also entirely manageable. With proper materials, proper storage, and proper vigilance, your Best of the Mint set can remain as brilliant and beautiful decades from now as it was the day it left the U.S. Mint.

Collecting is ultimately about the joy of ownership, the thrill of the hunt, and the satisfaction of completing a set. But that joy is best preserved — pun intended — when we take the time to protect what we have acquired. Inspect your sets. Upgrade your storage. Learn the signs of environmental damage. And when in doubt, ask a professional.

Your coins cannot protect themselves. That responsibility falls to you. Handle it with the same care and passion that led you to collect in the first place.

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