Coin Toning

Naturally toned 1907 Barber quarter courtesy of Adrian Crane ("anaconda.rare.coins")

IN A NUTSHELL: Toning can add natural beauty, and value, to coins. Or it can be the result of tampering by a coin doctor. There are ways to tell.


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.


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.

Toning on copper and its alloys is often called patina, though all toning is a type of patina, or coating. Brown or black patina on copper is caused by copper oxide, cupric oxide, or cuprous oxide, green or blue-green by copper sulfate or copper sulfides, and greenish blue by copper carbonate. "Bronze disease," which appears as a powdery green or blue-green on ancient bronze coins and consists of cuprous chloride or cupric chloride and hydrochloric acid, can eat away a coin's surface.

Ancient bronze coins can pick up an attractive "earthen" or "desert sand" patina. This sandy beige appearance over all or part of the coin's surface results from the deposition of microscopic grains of silicate from sand or sandy soil.

Gold, the least chemically reactive metal, aside from dulling slightly generally stays the way it is over even thousands of years. But the copper or silver that modern gold coins is typically alloyed with can tone, turning the color an attractive deep orange.

Some gold coins over time pick up subtle light brown or orange-brown streaks or spots, called copper spots or carbon spots (though carbon plays no role in their formation), which may have been caused by incompletely mixed copper in the alloy, by airborne contaminants, or by someone having breathed or sneezed on the coin. Unless copper spots are particularly conspicuous and offputting, they doesn't affect the value of gold coins. Toned gold coins with a "cloudy" affect are usually artificially toned, according to Campbell.

Ancient gold coins, when unearthed, can be covered with encrustations (dirt, grease, organic matter, salts, etc.) just like other coins. Gold coins uncovered from ship wrecks can have minutely pitted surfaces from the corrosive effects of salt water. Such coins can look like cast counterfeits.

Nickel generally tones only slightly, typically becoming hazy gray though sometimes light golden or pale blue. Nickel coins can also pick up color as a result of PVC contamination from being stored in soft vinyl flips. On nickel, wild rainbow toning, in which multiple colors progress from one to another, is usually artificial.

Aluminum (aluminium to the Brits and most of the rest of the world) typically tones a dull, unattractive gray.

The color of the toning on any coin is a factor of how advanced and thick the film of toning is. Early toning on silver coins is yellow, with the colors progressing to magenta (purplish red) to cyan (greenish blue) to black. The color results from "thin film refraction" or "thin film interference," the refracting of different wavelengths of light waves through the film. This is the same color effect that appears with soap bubbles and when a thin layer of oil lays on top of a puddle of water.

Different coin types tone in different ways. Morgan dollars tone more beautifully than Peace dollars because the planchets of the latter were given a more concentrated acid bath at the Mint. Walking Liberty half dollars tend to acquire unbalanced toning as a result of their asymmetrical design. Many commemorative halves from the 1930s have "tab toning" resulting from their original cardboard holders.

The same coin types can also tone in different ways. The toning of any given coin depends on a host of different factors, including how it was handled (oil and dirt from fingers and hands), how it was stored (canvas bag, paper bag, envelope, exposure to rubber band or glue, cardboard album, cardboard 2x2 holder, etc.), the quality of the external environment (heavily polluted, high humidity, sunlight, outgassing from different types wooden cabinets and bureaus, etc.), and external contaminants (different types of dust and dirt, grease, spilled coffee or beer, rain, moisture from sneezes and breath, and other stains whose consequences may be blatant or subtle).

Many unattractively toned silver coins are "dipped" in a thiourea solution, such as E-Z-Est Coin Cleaner, to remove the toning. If done properly, a white dipped coin can be attractive. If overdipped, a high-grade coin loses its luster and takes on an unattractive flat, lifeless look. If a coin isn't rinsed properly after dipping, it can pick up unattractive spotting or staining over time. Even properly dipped coins don't tone the same way later as coins with original surfaces, typically turning gray rather than colorful.

Artificial toning

Because attractively toned silver coins are desirable to many collectors, they usually carry a premium and sometimes a huge premium. This is particularly true with coins that have "monster toning" (wild toning), "target toning" or "bullet toning" (colors that change from the coin's periphery in toward to the center), "rainbow toning" (multiple colors), or "iridescent toning" (shimmering, with the color pattern varying with the viewing angle). Such coins are even graded higher by the grading services, which "market grade" according to a coin's overall eye appeal.

This motivates some people to artificially tone, or doctor, coins. Other times coin doctors artificially tone a coin to hide hairlines from a prior cleaning, scratches, contact marks, or even repair work.

The difference between natural toning and artificial toning isn't always clear-cut. Most toning results from human intervention (which is one definition of "artificial"), from placing a coin in contact with a man-made material such as a U.S. Mint canvas bag, an old Wayte Raymond coin album, or a traditional felt-lined coin cabinet.

Most people, however, regard toning as artificial when there's a deliberate attempt to impart it over a short time, such as baking a coin in an oven (alone or in a potato), blasting it with a blow torch, placing it in a covered bowl with crushed match heads (these coins smell!), blowing cigarette or cigar smoke on it, thumbing it with nose grease, or soaking or painting it with bleach, acid, or a sulfur-containing chemical. The gray area involves deliberately toning a coin with longer-acting techniques such as setting it for several months on a window sill in the sun, placing it on a block of oak wood in the sun, wrapping it in tissue paper, or sealing it in an ordinary high-sulfur envelope.

Coin collectors generally prefer modern coins to have natural, untampered surfaces (collectors of ancient coins are much more tolerant). The grading services do a good if not perfect job of detecting artificial toning (AT), which is one of the reasons many collectors buy older, higher-end coins in slabs. Among coin doctors, indication of a job well done is getting their AT coins in the slabs of the top grading services, PCGS or NGC, which happens not infrequently.

Some collectors are afraid of toned coins, says Mark Salzberg, president of the coin-grading service NGC. "It simply doesn't make any sense," he wrote in an article titled "The Virtues of Toned Coins," which appears at the Web site Coin-Gallery Online. "It's only natural that old coins, particularly silver pieces, acquire various degrees and shades of color over time. This is one of the most charming qualities of antique coins that distinguish them from more recent issues, and I believe collectors who don't already do so should learn to appreciate the virtues of toned coins."

To be fair, collectors have legitimate cause for being concerned about some toned coins. In his video How to Tell Artificial Toning on Coins, available for loan from the American Numismatic Association, Campbell says the following are AT tip-offs:

  • Circular toning spots resulting from the beading of the toning liquid that was used.
  • Colors that blend together out of sequence. With naturally toned coins, the progression is yellow then magenta (pinkish red) then cyan (blue-green).
  • Toning that appears only on the tops of the lettering and devices and not in the coin's recesses.
  • Wild "circus" colors -- on 90 percent silver coins, for instance, army green, bright pumpkin orange, and robin-egg blue.

According to PCGS's book
Coin Grading and Counterfeit Detection, the following are other indications of artificial toning:

  • The toning floats on the surface of the coin rather than having depth and being bonded to the metal.
  • The toning occurs over hairlines or other marks.
  • The toning exhibits bright "crayon" colors.
  • The toning has a yellow-brown, smoky appearance, indicating it was caused by cigarette or cigar smoke.

More on toning

Fake Rainbow Toned Coins

The Virtues of Toned Coins

eCoinPrices' Toned Coins

Corrosion Doctors' Silver Artifacts

Toned Coin Collectors Society


Coin Fraud

Counterfeit Coins

Grading Services

Coin Toning

Coin Cleaning

Coin Prices



Coin Holders

Coin Photography

Pocket Pieces

Coin Jewelry

Ancient Coins

Ancients Market

Ancients Grading

Attributing Ancients

Language and Ancients

 Looting and Coins

Coin sites:
Coin Collecting: Consumer Protection Guide
Glomming: Coin Connoisseurship
Bogos: Counterfeit Coins

© 2013 Reid Goldsborough

Note: Any of the items illustrated on these pages that are in my possession are stored off site.