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Detecting Doctored Coins, Part 1


This originally toned Barber half dollar has even and deep coloring.
This originally toned Barber half dollar has even and <i>deep</i> coloring.

Reprinted with permission from Professional Coin Grading Service (PCGS). Excerpt taken from The Official Guide to Coin Grading and Counterfeit Detection


"Coin doctors" have become increasingly active in recent years in the rare-coin marketplace. Unfortunately, their role has not been to cure the market's ailments, but rather to spread an epidemic: the alarming proliferation of coins that have been chemically treated, or otherwise tampered with, to make them appear better-and more valuable-than they really are.

The "doctoring" of coins is a special concern as well as a constant challenge for PCGS. Over the years, practitioners of this black art have become ever more sophisticated in their methods, making it harder and harder to distinguish their wares from original, untreated coins. The PCGS grading staff identifies and intercepts the great majority of these coins when they are submitted for certification, returning them to their consignors as ungradable. Even with all of their expertise and vigilance, however, graders are occasionally fooled and certify one of these coins. When that happens, the company's guarantee covers any loss incurred by the ultimate purchaser. However, the fact that it happens at all is testament to the seriousness of the problem. It also serves to underscore the value of certification in a marketplace where such dangers are all too common.

Lumped with doctoring is the cleaning of coins that really do need it. This is an area of much confusion, as evidenced by letters written to coin publications about coins that have been graded and placed in holders after being "cleaned" by dipping them in a commercial solvent or dip. Not all coins that have been altered by chemicals are considered doctored. No matter how the results are achieved, many coins have been improved by judicious cleaning with commercial dips, solvents, or plain soap and water. PCGS grades many coins that have had their surfaces altered by the removal of "problems," perceived or otherwise. The coins it does not grade are the ones altered by adding substances to the surface or altering the surfaces by physical methods.

Fooling with Mother Nature

"All coins are doctored," an astute numismatist once observed. "It's just a matter of degree and by whom Mother Nature or Joe Dipper." His point, one worth pondering, is that coins by their very nature are subject to chemical change because they are made from metals which, to a greater or lesser degree, are reactive. The surfaces of a coin begin to react with the environment from the very moment the coin is struck. Depending on how and where it is stored, the coin may change very little over time or, conversely, undergo a radical transformation. Sometimes the change is positive-spectacular color from a reactive holder. Other times it is very negative-PVC damage, salt-water damage, or other intrusive damage.

There is, however, a fundamental difference between the natural changes that occur in a coin's appearance because of environmental factors, on the one hand, and the artificial changes wrought by the intervention of larcenous profiteers who are, quite literally, fooling with Mother Nature to perpetrate a fraud. Natural toning, for instance, can greatly enhance the appearance of a coin in the eyes of many observers by embellishing its original color with dazzling rainbow hues. Artificial toning, by contrast, tends to be less attractive and is used all too often to conceal important flaws that could lower a coin's value if these flaws were visible. This, in fact, is one of the major ways in which coins are doctored: chemicals are used not to remove something from these coins, but to hide or obscure a problem.

Nearly every chemical known to man has been applied to the surfaces of coins to "improve" their look, and they have been subjected to bizarre and often ingenious forms of treatment, such as being washed in sulfur shampoo, blasted with cigarette smoke, even baked inside Idaho potatoes covered with corn oil! Some of the techniques are primitive, to be sure, but they can be effective in deceiving the unwary. And some of them are subtle and hard to detect.

Preservation or Exploitation?

Is doctoring inherently wrong and reprehensible? After all, no one cries "Foul!" when a painting is restored, and that involves the use of artificial means to enhance a collectible. Nor is there an outcry when museums "expertly clean" their ancient coins. At one time, in fact, it was common practice even among professionals to clean U.S. coins. It has been reported that coins in the National Numismatic Collection at the Smithsonian Institution were "polished to a high gloss" three times by the start of the twentieth century. In the early days of U.S. coin collecting, and even into the early 1900s, many hobbyists cleaned their coins with little regard for the consequences. The coins in some early U.S. collections were stored in wooden coin cabinets and regularly wiped to "improve" their look, giving rise to the term "cabinet friction." Today, these practices would be abhorrent to many-but at the time, they were accepted and looked upon as forms of enhancement as well as preservation.

The key difference between all of these practices and most of today's coin doctoring is that many of those engaged in such activities today are doing so for fraudulent gain. They are seeking to mislead others-the grading services and prospective purchasers, in particular-into accepting their coins at excessively high grade and price levels by disguising the deficiencies of those coins.

Beyond the issue of intent, the practice of doctoring can often be harmful to the health of the coins. Some of the processes and chemicals applied to coins actually do help preserve them in certain cases. The problem is, many of them do not. When an organic solvent such as alcohol or acetone is used to remove damage from the surfaces of coins that were stored in PVC flips, those coins are not only improved, but probably saved from ruin. On the other hand, the use of abrasive or corrosive chemicals can directly cause irreparable damage, rather than save the coin. This damage may not be apparent at first, but over time the coin may change as the chemicals further react with the coin's metals. The instability of many altered coins is noted only with the passage of time, sometimes too late to "save" the patient.

Doctoring is practiced in several ways. Three of the major methods are artificial toning, surface alteration, and etching. No analysis of the subject could be totally comprehensive, since new techniques probably are being tried every day. However, this chapter will examine in detail the basic techniques coin doctors practice. It also will tell you how to recognize these practitioners and how to develop skills to avoid their deceit. When a coin's surfaces are doubtful and it is being offered at a bargain price, a red flag is raised. When something seems too good to be true, it probably is.


All U.S. coins tone to some degree. How and to what degree are determined by various factors. Their metal content, where and how they are stored, and atmospheric conditions play the biggest roles in determining the depth and color of the toning. When acquired naturally over time, toning is often viewed as a positive attribute of grading, unless it becomes too dark, thick, mottled, or splotchy. When the toning results from the application of chemicals to the surface of a coin over a short period of time, perhaps with the use of heat to speed the process, the coin is said to have artificial or questionable toning.

The most obvious difference between natural and questionable toning is the way in which the toning "lies" upon the surface of a coin. When an original coin tones over time, the toning appears to be attached to the surface from the "bottom up." There is an appearance of depth to the toning and the colors are rich and natural looking. When a coin is toned quickly by the introduction of chemicals and/or heat to the coin's surfaces, the toning floats on the surface and the color lacks depth. The toning appears shallow and not "attached" to the surface, as with original color. The colors associated with this type of toning tend to be unnatural-looking, often called "crayon" colors because they look as though they were "colored" on the coin's surface-weak pastel colors "painted" by a first-grader.

Naturally Retoned Coins

Many coins that were cleaned in the past have since retoned naturally. In error, these are sometimes said to be questionably toned. This is a difficult area, since there is a very subtle difference between cleaned coins that have toned naturally and coins that have had the toning process enhanced by chemicals and/or heat. This is further discussed in chapter 5, Elements of a Coin's Grade, under the section about second toning. Because there are so many factors involved in original and artificial toning, discussion of every color and type of toning is impossible. However, understanding the processes of original and artificial toning is essential in recognizing the differences.

Once the original surface is removed from a coin by some type of commercial dip or cleaning, toning will no longer "adhere" in the same way it does with original coins. There are several chemical and physical reasons for this. One of the main reasons is that in coinage alloys, the subordinate metal tends to "leach" out or migrate to the surface. When the coin is cleaned, the first several layers of molecules are removed-and if leeching has been occurring for a substantial period of time, more of the minority metal is removed by any cleaning. Because the mix of the metals is now different, any new toning, whether natural or artificial, will be different and will adhere differently from the original toning.

A cleaned coin also will have "slicker" surfaces at times, probably due to residue from the cleaning compound and/or the "flattening" of the flow lines. These flow lines-or stress lines, as they sometimes are called occur when the metal flows into the recesses of the dies upon striking. This provides a rougher and minutely larger surface for the toning to adhere to-and when cleaning removes or "flattens" these flow lines, the toning will not adhere as easily and evenly as before. This contributes to the "floating" colors noted on second and artificial toning.

Showing True Colors

The chemicals in many of the old coin holders (the Wayte Raymond and Meghrig holders, for example) are responsible for the bright, usually peripheral, rainbow colors seen on many coins from old-time collections. These are among the colors that coin "chemists" try to duplicate with their concoctions. Another source of sometimes beautiful colors is the tissue in which the Mint wrapped Proof coins, and occasionally Mint State examples, from the 1850s onward. These colors, too, are widely imitated. However, these imitation colors are never quite right and do not "lie" correctly.

Toned original coins usually can be identified as such without much difficulty. However, there is little obvious difference between lightly cleaned coins that have retoned naturally over many years and coins that have been enhanced with chemicals and/or heat. By examining coins that you know have toned or retoned naturally over many years and comparing these with chemically enhanced coins, you will gain familiarity with the often subtle differences between these types of toning. You might also consider conducting your own experiments with inexpensive coins, applying nontoxic chemicals to their surfaces, then studying the reactions that occur. The results of such experiments will provide greater insight into the characteristics of artificial toning. How the colors and toning "lie" on the surfaces is one of the easiest-learned tools of the trade.

Chemicals, such as sulfur compounds, often result in "crayon" colors as opposed to more natural-looking greens, blues, reds, and yellows. Also, these "artificial" colors often do not blend as evenly as do original colors. When the colors are splotchy or uneven, there is a good chance Mother Nature did not cause them. Regardless of the process used, when the colors "float," have unusual lines, and are uneven, the coin is probably artificially enhanced. Sometimes these colors are applied just to the periphery, while other coins have the entire surface treated. Tab toning has also been simulated by chemically treating an original holder and applying heat to speed up the toning process. These are sometimes very deceptive, as the "tab" in the center of a coin is often taken as "proof' that a particular coin is original. Again, this applied toning will "float" and usually will have colors not seen on originally toned specimens. Other coins are noted with mottled toning, which often is applied over light original toning to make the colors appear "deeper" than they actually are. These mottled-toned coins usually have colors that are just a little off" crayon" colors or unusual blues or greens. Another form of added toning is often seen on Proof coins that have had the toning "rubbed" off of the high points. Toning is added to the "rubbed" areas, often blending quite well with the original toning. This is occasionally seen on Mint State coins as well.

Another type of artificial toning used to hide defects is the kind produced by "smoking" or "hazing" a coin by bombarding it with cigarette or cigar smoke. This method leaves a filmy, usually slightly opaque haze on the surface of a coin-a look that is sometimes described as "smoky." Hazy toning also can be acquired naturally through storage in flips or envelopes. If the area affected by the haze is localized over marks or hairlines, it probably was applied artificially. This type of alteration could just as easily be listed in the next section on surface alteration techniques, since toning usually is associated with more vivid colors, and this technique results in a milky white to a slightly creamy-white appearance.

For a look at detecting sophisticated surface alteration techniques, click on Detecting Doctored Coins, Part Two

Artificially toned 1882 Liberty Seated quarter. Obverse: Light color was probably added by sulfur or related chemicals. Reverse: Nothing <i>heavy</i> in this toning, just light pastel.

Artificially toned 1882 Liberty Seated quarter. Obverse: Light color was probably added by sulfur or related chemicals. Reverse: Nothing heavy in this toning, just light pastel.

Artificially toned Barber with <i>crayon</i> colors that <i>float.</i> Note the color is missing and lacks depth around the devices, such as the stars and lettering.

Artificially toned 1882 Liberty Seated quarter. Obverse: Light color was probably added by sulfur or related chemicals. Reverse: Nothing heavy in this toning, just light pastel.

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