Zinc Rot vs. Verdigris: How to Tell the Difference on Modern Pennies

If you’ve searched enough penny rolls, you’ve seen it. Coins that look like they’ve melted, bubbled, or turned a crusty green. Most people call it all the same thing: corrosion. But not all corrosion is created equal.

Zinc rot and verdigris both eat away at coins, but they start for different reasons and tell you very different things about the metal underneath. Knowing the difference can help you decide what’s worth saving and what belongs in the return pile.

In this post, we’ll look at how to spot each one, what causes them, and why only one can sometimes be stopped.

What Is Zinc Rot (and Why It Happens)

Zinc rot is what happens when the copper coating on a modern penny breaks down and the raw zinc underneath starts to corrode. It’s a problem unique to coins made after 1982, when the U.S. Mint switched from solid copper to copper-plated zinc to save on metal costs.

Once that thin copper layer is breached, whether from a scratch, chemical exposure, or a weak spot from the minting process, the zinc reacts with moisture and air. It starts to bubble and form gray or white powdery spots that eat outward. You’ll often see it under the surface, giving the coin a swollen or blistered look.

Unlike verdigris, which forms on the surface and can sometimes be stabilized, zinc rot destroys the metal from within. Once it starts, there’s no reversing it. The coin will eventually crumble apart.

Verdigris: The Green Stuff That Looks Worse Than It Is

Verdigris shows up as green or blue buildup on a coin’s surface. It’s the result of copper reacting with moisture, oxygen, or acids in the environment. You’ll see it on both older bronze and modern copper-plated coins, usually around the lettering, date, or in tight spots like the edges of Lincoln’s jacket.

Unlike zinc rot, verdigris is a surface reaction. It eats outward, not inward. That means it can sometimes be stabilized or removed safely with proper care. It’s a form of environmental damage, but not the worst kind. A coin with light verdigris can still look good and hold collector interest if it’s handled correctly.

The key difference is that zinc rot destroys metal from the inside, while verdigris just changes the outer layer. One is a death sentence. The other is just a warning sign.

How to Tell Zinc Rot from Verdigris

At first glance, both look like corrosion, but there are a few easy ways to tell them apart.

Verdigris is green or blue, often smooth or waxy, and it usually appears in small patches or thin films on the surface. It clings to copper areas and can be lifted gently with acetone or distilled water if caught early.

Zinc rot is gray or white, with raised bubbles or rough, cratered spots. It often spreads under the copper plating and distorts the coin’s shape. If you see a coin that looks puffed up or flaking apart, that’s zinc rot. Once it starts, it never stops.

A magnifier helps, but even without one you can spot the difference by color and texture alone. One looks like oxidation. The other looks like decay.

When to Save It and When to Let It Go

A little verdigris isn’t the end of the world. You can sometimes stabilize it with acetone or just leave it alone if it’s light and stable. Coins with honest aging still have story and eye appeal.

Zinc rot, though, is terminal. Once the metal starts to swell or crumble, it’s done. No cleaning or soaking will fix it, and trying usually makes it worse. When you see it, pull the coin, study it, and move on. That’s part of learning the life cycle of modern cents.

The longer you collect, the faster you’ll spot the difference. And when you do, you’ll stop wasting time trying to save what’s already gone and focus on preserving what’s still worth keeping.