How to Maximize Profits Selling 90% Silver Coins with PVC and Verdigris Concerns at Auction

Selling on eBay is a completely different game than consigning to a major auction house. I’ve spent over two decades watching that difference play out at the gavel, and positioning your coin correctly is the only way to see the highest hammer price.

As an auction house director, I’ve examined thousands of 90% silver coins over the past twenty years—Walking Liberties, Franklin Halves, and Kennedy Halves. Each one presents unique conservation challenges that directly impact its auction performance. One of the most common questions I get from consignors? What is that greenish deposit? Is it verdigris? Is it PVC? And critically, how does cleaning or treating the coin affect its numismatic value when it hits the auction block?

The answer to that last question is far more nuanced than most collectors realize. It sits right at the intersection of chemistry, grading standards, and auction strategy. I’m going to walk you through exactly how we position 90% silver coins with surface concerns for maximum profit—from pre-consultation through the hammer fall—so your coin’s eye appeal really shines.

Understanding the Chemistry: Verdigris vs. PVC on 90% Silver Coins

Why Terminology Matters at Auction

Before we talk about positioning a coin for sale, we need to get the science right—because the language you use in a catalogue description directly affects buyer confidence and final price. In the strictest chemical sense, verdigris is a copper compound, a mixture of copper salts like basic copper carbonate, formed through a purely mineral reaction. It needs a copper-rich alloy to develop.

90% silver coins contain 10% copper, which is enough to raise the question, but not typically enough for true verdigris to form under normal circumstances. When collectors see a green deposit on a silver coin, they are most likely dealing with PVC residue—polyvinyl chloride contamination from old coin flips, albums, or holders. PVC goo can form greenish deposits that collectors loosely call “verdigris,” but chemically, it is an entirely different beast.

Here is why this distinction matters for auction:

• PVC deposits are organic in the sense that they come from synthetic polymer contamination and can be dissolved with acetone, preserving the coin’s natural patina.
• True verdigris is an inorganic copper salt that cannot be removed by acetone and requires acidic treatments like sulfuric-acid-thiourea dips.
• Corrosion on silver—sometimes verdigris-like in appearance—may need ammonia-based solutions or professional conservation to protect its provenance.

When I’m evaluating a consignment, I insist on clear photographs and an honest disclosure of any surface concerns. Why? Because a coin that has been improperly cleaned or chemically treated before reaching my auction house will net the consignor significantly less—sometimes 30-50% less—than a coin with honest, natural surfaces and full mint condition.

Buyer’s Premiums and Seller’s Fees: The Hidden Math of Auction Profits

How Premiums Affect Your Bottom Line

Every consignor needs to understand the fee structure before placing a coin in our auction. At our house, the standard buyer’s premium is structured like this:

• 1-2% on lots up to $5,000
• 1.5% on lots from $5,001 to $25,000
• 1% on lots above $25,000

This premium is added to the hammer price and paid by the buyer, but it directly influences bidding behavior. A coin with a $500 estimate and a 2% buyer’s premium costs the buyer $510—a psychological threshold many bidders round up to $525 or $550. Understanding this dynamic is essential when you’re deciding whether to clean, conserve, or leave a coin as-is to protect its collectibility.

On the seller’s side, our consignment fees typically range from 10-20% of the hammer price, depending on the value of the lot and the scope of catalogue inclusion. A high-grade 90% silver coin with professional photography and a detailed description might qualify for a reduced seller’s fee—which is why investing in proper presentation pays for itself.

The Real Cost of Over-Cleaning

I’ve seen consignors spend $50 on a coin cleaning attempt that cost them $500 in unrealized value. When acetone or other solvents are used improperly on a 90% silver coin, the risk isn’t just chemical—it’s numismatic. Over-aggressive cleaning can:

1. Remove the natural toning that grade-conscious collectors prize
2. Scratch the surface with Q-Tips or abrasive materials, dropping the coin from mint state to about uncirculated and ruining its luster
3. Strip away original surface texture that authentication services use to verify provenance
4. Reduce the coin’s appeal to the “original tone” segment of the market, which often commands 20-40% premiums over cleaned examples

In my experience grading and auctioning silver coins, an honest, naturally toned example with minor PVC residue—properly disclosed in the catalogue—will almost always outperform a “cleaned bright” example of the same date and mint mark. The market rewards authenticity and a strong strike.

Auction Timing: When to Consign Your Silver Coin

Seasonal Market Dynamics

Timing is one of the most powerful levers a consignor has. Silver prices fluctuate based on industrial demand, geopolitical events, and bull market sentiment, and the auction calendar creates its own micro-cycles.

In my experience, the best windows for consigning 90% silver coins are:

• January-March: Post-holiday liquidity. Collectors have sold holiday gifts and are looking to reinvest. Silver coin demand consistently spikes.
• June-July: Summer auction series attract international bidders. European and Asian collectors actively compete for U.S. silver commemoratives and circulation strikes, especially a rare variety that might be hiding in a collection.
• September-October: Pre-winter collecting season. Many collectors finalize their sets before year-end tax considerations take effect.

Conversely, I generally advise against consigning during the first two weeks of December—bidders are distracted by holiday obligations, and competition drops by as much as 15-20% compared to our January sessions.

The Role of Silver Spot Price

When silver spot prices are rising, we see increased participation from melt-value-driven buyers who may bid aggressively on any 90% silver coin, regardless of grade or date. When prices are flat, the market becomes more discriminating—and the quality of your coin’s presentation (photography, description, honest grading) becomes the primary differentiator.

This is exactly why I recommend that consignors wait for a spot price rally before submitting coins that have any surface concerns. A coin with minor PVC residue that might be worth $120 in a subdued market could fetch $155-$180 when silver is trending upward and bidders are less picky about minor surface characteristics, especially if the provenance is solid.

Professional Photography: Your Coin’s First Impression

Why Images Drive Hammer Prices

I cannot overstate the importance of professional photography in the auction process. When a potential bidder scrolls through our online catalogue, they are making split-second decisions based on images. A coin with clear, well-lit photographs—even one with minor surface imperfections—will consistently outperform a coin with poor images, regardless of the underlying grade. That is where eye appeal starts.

Our studio photography protocol for 90% silver coins includes:

• Obverse and reverse at 90-degree angles—showing the full design fields and rim
• 45-degree detail shots—capturing any toning, surfaces marks, or areas of concern
• Macro photography of the specific area in question—if there’s a green deposit or residue, we photograph it honestly so bidders know exactly what they’re getting
• Consistent lighting at 5000K—neutral white light that reveals true toning colors without distortion
• Scale reference in every image—typically a coin measuring tool or known-dimension object

The Disclosure Advantage

Here’s a counterintuitive insight from my years directing auctions: honest disclosure of minor surface issues actually increases buyer confidence and final price. When a catalogue entry reads “Minor PVC residue visible in the reverse fields—see detailed macro images,” it signals to sophisticated collectors that the consignor and auction house are being transparent. This transparency builds trust, and trust drives competitive bidding.

I’ve personally overseen auctions where a 90% silver coin with minor, honestly disclosed PVC residue sold within 5% of a pristine example of the same date and mint mark, while a coin with undisclosed cleaning damage sold for 35% below estimate. Mint condition matters, but honest collectibility matters just as much.

Catalogue Descriptions: The Art of the Narrative

Writing for the Right Buyer

A catalogue description is not merely a list of facts—it is a sales document. When I write descriptions for 90% silver coins with surface concerns, I structure them to address the informed buyer’s concerns while highlighting the coin’s strengths:

1. Opening statement: Identify the coin by date, mint mark, denomination, and grade in the first sentence. This is what buyers search for.
2. Surface description: Honestly describe any toning, residue, or cleaning. Use precise language—”faint golden toning on the obverse” is far more appealing than “slightly cleaned.”
3. Conservation note: If the coin has been
   

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