Among coin collectors, toning is almost as controversial as market grading. Some like toning, some don’t, some toning is real, some is not.

As a general rule, toned coins tend to be preferred more by advanced collectors than beginning collectors, while coins that look the same way they looked when they came from the Mint tend to be preferred more by newcomers. “People buy the color, experience, life of the coin, not just the technical grade,” says Bob Campbell, former ANA president and coin dealer who sells toned coins. “Beginning collectors like blazing white coins. More advanced collectors like beautifully toned coins.”

There are exceptions to this, of course, with some advanced collectors preferring their silver coins blast white. Both toned and untoned coins have their attractions, though the attraction of a beautifully toned coin is undeniable.

A beautifully toned coin is a coin that has aged well. The magnificent aging of silver, in particular, is analogous to the magnificent aging of deciduous leaves every year, in the right climates, before they turn brown, the brilliant yellows and reds of the fall’s foliage. This doesn’t always happen with either leaves or silver. You need the right environment. When it does happen, it pleases the eye. Color is simply more appealing than gray.

The appreciation of toning is often a sensibility that comes with time, similar to appreciating the relatively small differences in uncirculated grades, say between a 64 and a 66. When you first start out, a coin with toning looks old or unnatural. Then you begin to appreciate the sometimes marvelous ways that time can paint a beautiful picture on coins.

Toning is just the numismatic way of saying tarnish. Ironically, like rust on iron, toning on silver and bronze is a form of corrosion. What happens with silver and bronze is similar to what happens with iron, only it’s a slower process with bronze and an even slower process with silver. Like rust, the toning on coins gets thicker over time.

Eventually bronze and silver coins, over perhaps hundreds of thousands of years depending on the chemical makeup of their environment, will transform into 100 percent of the reactive products, as the toning becomes thicker and thicker until it becomes the entire coin. The chemical reactions won’t stop here, as entropic forces cause the material to become more and more random and disordered until it’s returned to the Earth. Dust to dust.

Not all toning is beautiful. With some coins toning can indeed be brilliantly and spectacularly colorful. With other coins toning can only subtly enhance eye appeal. With still other coins, toning can be dark, streaky, splotchy, spotty, uneven, or otherwise ugly, making the coin look like an algae-stained remnant from the Blue Lagoon. Because such toning when extreme is considered environmental damage, the top grading services won’t grade these coins.

Toning is an alteration of the chemical makeup and color of a coin’s surface. It takes place naturally over time as the metal reacts with chemicals in its environment, typically to various sulfur-based compounds. Or it can be induced artificially, and more quickly. Natural toning takes place more quickly in a warmer and more humid environment.

Some contend that not all coins tone, silver or otherwise. If sealed in an airtight environment, the surfaces of a coin will deplete sulfur and other chemicals around it and stop toning after that. Intercept Shield coin holders are designed to intercept and neutralize sulfur and other contaminants and thus prevent toning.

Metals

Numismatic metals tone in different ways. Silver coins as a whole tone more beautifully than those made of other metals. Silver, exposed to the right environmental influences — to small amounts of hydrogen sulfur in the air or larger amounts in albums, envelopes, canvas bags, paper rolls, leather wallets or purses, rubber bands, and some glues and paints — can naturally turn subtle or sometimes brilliant shades of yellow, magenta, turquoise, and other colors before eventually turning black. The toning on silver is typically silver sulfide.

Ancient silver coins are often black when unearthed, the black surfaces typically caused by the sulfides formed by the rotting of organic matter containing such sulfurous amino acids as cysteine.

Though toning on silver is most often caused by sulfur, the word toning is sometimes used to describe other coloration on the surface of a coin, even stains or dirt. Silver can react with other substances such as chlorides in soil, producing silver chloride or “horn silver,” which typically appears as an unattractive black, gray, purple, or brown stain that projects slightly above the surface of the coin and smears easily.

The toning of silver coins is partly a factor of the other metals the silver is alloyed with, particularly copper. Ninety percent silver coins (most circulating U.S. coins) tone differently than sterling silver (British coins), triple nine-fine silver (American Silver Eagles), ancient silver coins, and most world silver coins. Silver coins can turn green from the copper they’re typically alloyed with, the green resulting from copper carbonate or copper chloride, though this happens more frequently with world and ancient coins that have a higher copper content than U.S. coins.

Copper is the most chemically reactive numismatic metal used in the U.S., and it and its alloys — bronze (primarily copper and tin) and brass (primarily copper and zinc) — usually turn from red to a dark and fairly unattractive brown. But copper can turn green as well (sometimes called verdigris). Sometimes copper and its alloys can pick up multiple subtle and attractive shades of red, brown, green, blue, and yellow.

Some lovers of early U.S. cents (large cents dating 1793 to 1857) love the look of toned copper. “Old copper, like beauty, appears to possess a certain intrinsic quality or charm which for many people is irresistible,” said Dr. William Sheldon in his 1958 book Penny Whimsy. But the marketplace as a whole prefers red. Early copper coins are more valuable if naturally red and untoned than red-brown, which in turn are more valuable than brown.

http://rg.ancients.info/guide/toning.html

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Images at Top: Naturally toned 1907 Barber quarter courtesy of Adrian Crane (“anaconda.rare.coins”)

biz bite: Dr. William Sheldon is responsible for devising the Sheldon Scale, a 1 to 70 numeric rating given to coins. 1 is the poorest, 70 is flawless, perfect. A graded, certified MS-70 coin is a perfect museum quality coin.

..for high-end coin collecting/investing: http://www.numisnetwork.com/bluetree