Verdigris: What It Is and Why It Shows Up on Coins

Verdigris is that weird green stuff you sometimes see on old copper or bronze coins. It can range from a faint, minty haze to thick, crusty blobs that look like the coin was stored in a compost pile. And while it might look kind of cool in certain lighting, it’s not a sign of anything good.

In the coin world, verdigris is considered a form of environmental damage, and it’s one of the most common reasons a copper coin ends up with a Details grade. But unlike general corrosion, which often comes from long-term exposure to moisture or acids, verdigris is usually a chemical reaction involving copper, oxygen, moisture, and various salts or contaminants.

In this post, we’ll break down what verdigris is, what causes it, how to spot it early, and what (if anything) you can do about it.

What Causes Verdigris on Coins?

Verdigris is a reaction between copper and environmental contaminants like moisture, oxygen, salts, and acids. It’s most often triggered by poor storage conditions or contact with harmful materials.

Here are some common causes:

• Humidity and Poor Storage: High moisture levels combined with airtight or non-archival containers create a breeding ground for corrosion.
• PVC Damage: Old flips made with PVC can break down over time, leaching chemicals that eat into the coin and leave behind thick green buildup.
• Salt, Sweat, and Skin Oils: Contact with bare hands or exposure to salty environments can leave residue that accelerates corrosion.
• Buried Coins or Ground Finds: Soil minerals and fertilizers introduce chemical reactions that form heavy verdigris over long periods.

It often starts slow, but once it takes hold it keeps spreading unless it’s removed.

How To Spot Verdigris on Coins

Verdigris usually shows up as green, blue-green, or sometimes even bluish-white patches on the surface of a coin. The texture and location can help you confirm what you’re seeing:

• Color: Bright or dull green is the most common, though it can look turquoise or bluish under certain lighting.
• Texture: It may appear waxy, crusty, or flaky. It’s usually not smooth like toning or tarnish.
• Location: Verdigris tends to form in low spots, like around lettering, between devices, or near the rim, where moisture and contaminants settle.

A light dusting of green is enough to get a coin labeled with environmental damage. If it’s built up into a crust or has started to pit the surface, the coin’s value can take a serious hit.

Grab a handful of old pennies from a jar, and odds are a few will have the telltale green crust starting to spread. It’s one of the most common forms of damage in circulated copper.

Can Verdigris Be Removed?

Yes, but it’s risky. Verdigris is often embedded in the surface of the coin and removing it can cause more harm than good. You might reveal pitting or discoloration underneath, and any cleaning method that alters the coin’s surface will usually guarantee a details grade.

Professional conservation services do exist, but they’re rarely worth it unless the coin is especially valuable. Some companies and experts specialize in removing verdigris or stabilizing coins, but results can vary and the cost often outweighs the benefit. Most collectors choose to leave coins with environmental damage alone unless it’s getting worse or threatening nearby coins.

There are household methods floating around, from olive oil soaks to more aggressive chemical treatments, but these should be approached with extreme caution and only on low-value coins. Once you remove the verdigris, you can’t undo the effects of overcleaning or altered surfaces.

What’s It Worth?

Verdigris almost always lowers a coin’s value, usually dramatically. Even a coin with great detail and eye appeal will take a hit if it has visible green corrosion. For common-date coins, it often pushes them into “only worth a few cents” territory. For scarcer pieces, it can still hold value, but usually at a steep discount.

The extent of the damage matters. A tiny green dot near the rim might just be a conversation point. A spreading, powdery mess across the whole surface? That’s a dealbreaker for most buyers. And once verdigris becomes active, it can be contagious. Stored coins nearby are at risk, which makes buyers even more cautious.

Some collectors are willing to take on the risk, especially if the coin has historical value or fills a tough hole in a set. But don’t expect strong prices unless the coin is rare enough to justify a gamble.

Final Thoughts

Verdigris might sound like an exotic word, but it’s just a fancy name for green corrosion, and it can be bad news for your collection. It’s not just a cosmetic issue. It’s a sign that your coin is breaking down, and it won’t stop unless it’s dealt with.

Whether you’re sorting wheat cents from a bulk lot or flipping through a dealer’s album, train your eye to spot it early. And if you already have coins with active verdigris in your collection, isolate them immediately. We’ll cover how to safely store those in the next post.

If you’re ever unsure whether a green spot is harmless or dangerous, lean toward caution. When in doubt, separate it out.