How to Properly Store and Preserve Coins: Lessons from a Mysterious 1963-D Cent and the Dangers of PMD

I’ve seen too many valuable pieces ruined by improper cleaning or storage. Here is how to keep your coins safe for the next generation.

Every collector has a story about the one that got away — not the coin they failed to buy, but the coin they ruined. I’ve examined thousands of pieces over the course of my career, and I can tell you without hesitation that the single greatest threat to a coin’s long-term numismatic value and historical integrity is not time itself. It is us. It is the well-intentioned collector who reaches for a metal polish, the hobbyist who slides a beautiful mint-state cent into a PVC-laden flip, or the newcomer who spends hours trying to determine whether a mysterious mark on a 1963-D penny is a rare variety or post-mint damage — and then, in frustration, tries to “fix” the coin with a brush or chemical solution.

The fascinating forum thread titled “One of One? Or, PMD?” — in which a collector discovered a 1963-D Lincoln cent bearing a raised symbol on both sides and spent weeks trying to determine its origin — is a perfect case study in why understanding preservation, toning, oxidation, PVC damage, and the eternal question of whether to clean or not to clean is absolutely essential for every collector, from beginner to advanced. Let’s use this thread as our launching point and explore the conservation principles that will protect your collection for decades to come.

The 1963-D Cent Mystery: A Masterclass in Observation

The collector at the center of this thread — known as newbuddy56258 — found something genuinely puzzling. A 1963-D Lincoln cent with what appeared to be a raised metal symbol on both the obverse and reverse. The initial hypothesis was exciting: could this be a one-of-one mint error? Had a mint employee somehow marked a die for inspection, producing a coin with an intentional raised symbol that escaped into circulation?

The forum’s experts, including the highly respected Sapyx, methodically dismantled this theory. Their reasoning is instructive for every collector:

• Mint protocol: If a die fails inspection, it is destroyed — not defaced and then used to strike coins. The U.S. Mint does not carve symbols into dies and then release those coins into circulation.
• Die mechanics: A mark carved or stamped into a die would create a raised mark on the struck coin, not an indented one. To create an indent on a coin via die modification, you would somehow need to add material to the die’s surface — a process that is extraordinarily difficult and impractical.
• The counter-punch explanation: A well-braced punch applied to a coin displaces metal downward, pushing it outward on the opposite side. This creates a flattened spot on the reverse directly underneath where the punch struck the obverse — exactly what was observed on this coin.
• The optical illusion factor: After extensive back-and-forth — including debates about lighting angles on the date versus the symbol — the original poster ultimately conceded under microscopic examination that the symbols were not raised at all. They were the result of post-mint damage (PMD), and the appearance of being raised was a trick of the light.

This entire exchange is a beautiful example of the scientific method applied to numismatics. But it also highlights something critical for preservation: the temptation to “enhance” or “investigate” a coin’s surface with physical or chemical intervention is one of the most dangerous impulses in this hobby. Let’s talk about why.

Toning: Nature’s Patina and Why You Should Never Remove It

One of the most misunderstood aspects of coin conservation is toning. Toning is the natural discoloration that occurs on a coin’s surface over time as the metal reacts with sulfur compounds, moisture, and other elements in the environment. On silver coins, toning can produce breathtaking rainbow hues — magentas, blues, golds, and greens — that are not only beautiful but can actually increase a coin’s collectibility and market value dramatically.

What Causes Toning?

Toning is essentially a controlled form of oxidation. When silver or copper surfaces are exposed to trace amounts of hydrogen sulfide in the air, thin layers of silver sulfide or copper sulfide form on the surface. The thickness of these layers determines the color we see, due to the same light-interference principles that create oil-slick rainbows on water.

Key factors that influence toning include:

• Storage environment: Coins stored in paper envelopes, cardboard holders, or near certain fabrics will tone more quickly due to sulfur content in these materials.
• Humidity: Higher humidity accelerates chemical reactions on the coin’s surface.
• Metal composition: Silver tones differently from copper, gold, or nickel alloys. A copper coin like our 1963-D cent will develop a rich brown patina over time, while silver coins can display the full spectrum of rainbow colors.
• Time: Natural toning develops over years and decades. Artificial toning — achieved through chemical treatment — can sometimes be detected by experienced graders because it tends to look uneven, splotchy, or unnaturally vivid.

The Cardinal Rule: Never Clean a Toned Coin

I cannot stress this enough. If you have a coin with attractive, natural toning, do not attempt to remove it. I have seen collectors take a beautifully toned Morgan dollar worth $500 and turn it into a brilliant-but-scratched piece worth $20 with a single application of silver dip. The toning is part of the coin’s history. It is part of its character. And in many cases, it is a significant component of its eye appeal and market value.

Even “gentle” cleaning methods — baking soda paste, vinegar soaks, commercial dip solutions — remove microscopic layers of the coin’s original surface. This is permanent, irreversible damage. Grading services like PCGS and NGC will often mark cleaned coins with a “Cleaned” or “Improperly Cleaned” designation that can reduce value by 50% or more.

Oxidation: The Slow Enemy and How to Fight It

While toning is a form of oxidation that can be aesthetically pleasing, uncontrolled oxidation is a serious threat to a coin’s preservation. Oxidation is the chemical process by which metal atoms lose electrons to oxygen or other reactive elements in the environment. On copper coins, this produces the familiar green verdigris. On silver, it creates black tarnish. On steel or iron coins, it produces destructive rust.

How to Minimize Oxidative Damage

The key to preventing harmful oxidation is controlling the coin’s environment. Here are the principles I recommend to every collector:

1. Control humidity: Store your coins in an environment with relative humidity between 30% and 50%. Higher humidity accelerates oxidation; lower humidity is generally safe but can cause desiccation of organic materials in holders.
2. Avoid pollutants: Keep coins away from sources of sulfur, chlorine, and other reactive chemicals. This includes rubber bands, certain adhesives, and even some types of paint or varnish used in display cases.
3. Use inert storage materials: This brings us to our next critical topic — proper holders.
4. Handle coins properly: Always hold coins by the edges. The oils and moisture from your fingers can initiate localized oxidation that becomes visible within months.

PVC Damage: The Silent Killer of Coin Collections

If there is one thing that makes me shudder more than seeing a cleaned coin, it is seeing a coin with PVC damage. Polyvinyl chloride (PVC) was once the standard material for coin flips and holders. It was cheap, transparent, and readily available. It was also catastrophically bad for coins.

What PVC Does to Coins

PVC is not chemically stable. Over time, it breaks down and releases hydrochloric acid and chlorine gas. These compounds react with the metal surface of coins, producing a characteristic greenish, sticky, or waxy film that is extremely difficult — and sometimes impossible — to remove without damaging the coin’s surface.

PVC damage typically appears as:

• Green or blue-green spots or streaks on the coin’s surface
• A sticky or tacky residue that attracts dust and debris
• Hazy or cloudy areas that cannot be wiped away
• In advanced cases, actual pitting of the metal surface

I have seen entire collections of otherwise mint-state coins rendered nearly worthless because they were stored in PVC flips for decades. The damage is cumulative and progressive — the longer a coin remains in PVC contact, the worse it gets.

How to Identify PVC Holders

PVC flips and holders tend to be softer and more flexible than their safer alternatives. They often have a slightly “plastic” smell when you open a fresh package. If you have older flips in your collection that feel soft, sticky, or slightly cloudy, there is a good chance they contain PVC. Remove your coins from these holders immediately.

Proper Holders: Your First Line of Defense

Choosing the right storage materials is the single most impactful preservation decision you can make. Here is my hierarchy of recommended holders, from most to least protective:

1. Mylar (Polyester) Flips

Mylar flips — sometimes sold under brand names like “Archival Quality” or “Coin Flips” — are made from polyethylene terephthalate (PET) or polyester film. They are chemically inert, meaning they will not react with your coins’ metal surfaces. They are rigid enough to provide physical protection and clear enough to allow viewing without removal. This is the minimum standard I recommend for any coin you care about preserving.

2. Hard Plastic Holders (Capsules and Slabs)

For higher-value coins, hard plastic capsules or screw-top holders provide superior protection. These are made from acrylic or polycarbonate and are completely inert. They protect against physical damage, environmental exposure, and handling. Many come with foam inserts to prevent the coin from rattling around inside.

3. PCGS, NGC, or ANACS Slabs

If a coin has been professionally graded and encapsulated by a reputable third-party grading service, it is already in one of the best preservation environments available. These slabs are sonically sealed, made from inert materials, and designed to protect the coin for decades. Do not remove a coin from its grading slab unless you have a compelling reason to do so.

4. Albums and Pages

For circulated collections or lower-value pieces, coin albums with Mylar-lined pages are acceptable. Avoid albums with PVC-containing plastic slides or pages. Look for products specifically labeled “PVC-free” or “archival quality.”

Materials to Avoid

Here is a quick-reference list of materials that should never come into contact with your coins:

• PVC flips and holders (greenish, sticky residue over time)
• Rubber bands (sulfur content causes rapid tarnishing)
• Paper envelopes with high sulfur content (can cause uneven toning)
• Adhesive tapes or labels (residue is nearly impossible to remove)
• Wooden display cases with unsealed surfaces (wood off-gasses acids)

To Clean or Not to Clean: The Eternal Question

This is the question I am asked more than any other, and my answer is always the same: Do not clean your coins. But the reality is more nuanced than that, so let me explain.

Why Cleaning Almost Always Destroys Value

When you clean a coin, you are removing a microscopic layer of the coin’s original surface. This includes the original mint luster, the natural toning, and the microscopic flow lines created during the strike. Even the gentlest cleaning method — a soak in distilled water, for example — can alter the coin’s surface chemistry in ways that are visible under magnification.

Professional grading services have sophisticated methods for detecting cleaned coins. They examine the surface under various lighting conditions, looking for:

• Disruption of original mint luster
• Micro-scratches from abrasive cleaning
• Uneven color or surface texture
• Artificial brightness that is inconsistent with the coin’s age and composition

A coin that might grade MS-65 in its original state might be marked “Improperly Cleaned” and become essentially ungradeable after even a mild cleaning attempt. The value loss can be 90% or more.

The Rare Exceptions

There are a few limited circumstances where professional conservation may be appropriate:

• PVC removal: If a coin has been exposed to PVC and developed green residue, a professional conservator may be able to remove the residue using specialized solvents that do not damage the underlying metal. This should never be attempted at home.
• Environmental contamination: Coins recovered from shipwrecks or buried hoards may require professional stabilization to halt active corrosion. This is a specialized field and should only be performed by trained conservators.
• Museum-grade conservation: Institutional conservators have access to techniques and materials that are not available to individual collectors. If you have a historically significant piece, consult a professional.

What You Can Do Safely

If a coin is dirty but you want to improve its appearance for display purposes, here are the only methods I consider safe:

1. Distilled water soak: Soaking a coin in distilled water for a few hours can loosen surface dirt without chemical reaction. Pat dry with a soft, lint-free cloth. Do not rub.
2. Acetone soak (for organic residue only): Pure acetone (not nail polish remover, which contains additives) can safely remove organic materials like tape residue or grease from a coin’s surface. Acetone does not react with most coin metals. Soak briefly, then allow to air dry. Do not rub.
3. Proper handling: Simply handling coins with clean hands or cotton gloves and storing them properly will prevent most problems before they start.

Lessons from the 1963-D Thread: What Every Collector Should Take Away

The forum discussion about the mysterious 1963-D cent offers several important lessons that go well beyond the specific question of whether that particular coin was a mint error or PMD. Let me distill them into actionable takeaways:

1. Invest in Proper Magnification and Lighting

The original poster was ultimately convinced that the symbols on his coin were not raised — despite his initial conviction — only after re-examining the coin under a microscope. Good lighting and magnification are not luxuries; they are essential tools. A quality loupe (10x to 20x) and an adjustable LED light source will serve you far better than any cleaning product ever could.

2. Learn the Minting Process

Understanding how coins are actually made — how dies are created, how metal flows during striking, what kinds of errors can and cannot occur — is the single best defense against misidentifying post-mint damage as a rare variety. The expert who explained that a mark carved into a die would create a raised mark on the coin (not an indented one) was applying fundamental knowledge of the minting process. Resources like error-ref.com and educational videos on the minting process are invaluable.

3. Seek Multiple Expert Opinions

The forum thread demonstrates the power of collective expertise. No single person has all the answers, but a community of experienced collectors and professionals can usually arrive at the correct conclusion through reasoned debate and evidence. Don’t be afraid to post clear, well-lit photographs and ask for opinions. And don’t be afraid to be wrong — as the original poster graciously demonstrated when he acknowledged the optical illusion.

4. Preserve the Coin Regardless of the Verdict

Whether the 1963-D cent turned out to be a one-of-one mint error or post-mint damage, the preservation principles remain the same. Store it in a PVC-free Mylar flip or hard capsule. Do not attempt to clean it, enhance it, or “improve” it in any way. Document your findings and opinions, and keep the coin in a stable environment. If it is a genuine rarity, its provenance and proper care will only increase its numismatic value over time. If it is PMD, it is still an interesting conversation piece and a learning opportunity — and it deserves the same respectful treatment.

Building a Preservation-First Mindset

The best collectors I know share one trait in common: they think about preservation before they think about profit. They buy the right holders before they buy the coins. They set up their storage environment before their collection outgrows its current home. They educate themselves about toning, oxidation, and the dangers of improper handling before they make a costly mistake.

Here is my recommended preservation checklist for every collector:

1. Audit your current storage: Go through every coin in your collection and identify any PVC flips, rubber bands, or other harmful materials. Replace them immediately with Mylar flips or hard capsules.
2. Control your environment: Invest in a hygrometer to monitor humidity in your storage area. Consider silica gel packets or a dehumidifier if humidity exceeds 50%.
3. Handle with care: Always hold coins by the edges. Wear cotton gloves for high-value pieces. Never slide coins across surfaces.
4. Document everything: Photograph your coins under consistent lighting conditions. Record any unusual features, toning patterns, or marks. This documentation is invaluable for insurance purposes and for tracking changes over time.
5. Never clean: Write this on a sticky note and put it on your desk. Never clean your coins.
6. Educate continuously: Read books, watch videos, attend club meetings, and participate in forums. The more you know about the minting process, metal chemistry, and conservation techniques, the better equipped you will be to protect your collection.

Conclusion: The Legacy You Leave Behind

The 1963-D cent at the center of this forum thread may or may not be a genuine rarity. The consensus of the expert community is that it is post-mint damage — a counterstamp or punch mark applied after the coin left the Denver Mint. But the coin’s ultimate significance lies not in its market value or its error status. It lies in the conversation it sparked, the knowledge it generated, and the reminder it provides that every coin in our collections is a physical artifact with a history that deserves to be preserved.

Whether you are holding a circulated 1963-D cent or a pristine 1909-S VDB in mint condition, the principles are the same. Respect the coin’s surface. Respect its history. Store it properly. Handle it carefully. And above all, resist the urge to “improve” what time and nature have created.

The coins we collect today will outlive us. They will pass to our children, our grandchildren, and to collectors we will never meet. Our job is not to make them look new. Our job is to make sure they survive. Proper storage in PVC-free holders, controlled humidity, avoidance of chemical cleaners, and a deep understanding of toning and oxidation are not just best practices — they are our responsibility as stewards of these small but irreplaceable pieces of history.

I’ve examined too many collections where decades of careful accumulation were undone by a single afternoon of well-meaning but destructive cleaning. Don’t let that be your story. Preserve first. Preserve always. And let the next generation inherit the collection you’ve worked so hard to build — intact, authentic, and full of the character that only time can bestow.