A Guide to Selling Colorful & Toned Coins

The Science of a Toned Coin: Toning vs. Tarnishing

As coins age, their color can change in one of two ways. Understanding the difference is key to a coin’s value.

Tarnishing (Undesirable)

Tarnish occurs when a coin’s metal, usually silver, reacts with oxygen. This process forms a layer of silver-oxide, which typically appears as a dull, dark, or hazy gray coating on the coin. Over time, heavy tarnish can degrade the coin’s surface and will almost always lower its value.

Toning (Desirable)

Toning is a different, less common chemical reaction. It often happened when coins were stored for long periods in original mint bags or paper albums that contained trace amounts of sulfur. The coin’s silver reacts with the sulfur to form a thin, stable film of silver-sulfide.

This film acts like a prism, refracting light and creating the spectacular rainbow and pastel colors that collectors prize. We are especially interested in purchasing “Monster Toned Coins” that display incredible color, usually found on coins in higher, uncirculated grades.

To see stunning examples and get an authoritative explanation of the physics involved, check out our guide to Monster Toned Morgan Silver Dollars.