Gold Coin Grading: Seeing Spots Is Not Necessarily a Bad Thing

Posted on 3/21/2009

The experts at NGC share their thoughts about copper spots on gold coins, including how these spots can affect a coin's grade and what can be done about them. This article originally appeared in the Professional Numismatists Guild’s quarterly newsletter.

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Buyers of gold coins, unless they are seasoned numismatists, are frequently puzzled by the appearance of reddish spots or streaks on vintage gold pieces. Known in the coin business as "copper spots," this term pretty much sums up their nature. These spots and streaks are caused by concentrations of copper amid the overall gold composition.

United States gold coins minted for general circulation until 1933 are actually just 90 percent gold. The balance of their mass is made up of lesser metals that served to make the coins harder and thus more resistant to wear. After all, these coins were made to be used as money, not as collectibles, and frequent contact with one another during transport or while being exchanged in commerce caused them to become abraded and lose some of their mass. To slow this process, a blend of copper (mostly) and silver (in small amounts) was added to the gold to create the standard alloy typical of these older coins.

Ideally, this alloy blended completely, so that every area of the coin was uniformly 90 percent gold and 10 percent copper-silver. For the most part the US Mint was able to maintain this ideal mix, but in some instances the copper formed concentrated areas at a coin's surface. Being more reactive to the atmosphere than gold, these concentrations of copper slowly toned to a deeper red, which, when set against the overall gold color, results in various shades of orange to the eye.

If the concentrations are small, the result will be a tiny spot ranging in color from pale orange to vivid red. If, however, the coppery area was rolled out into the metal strip from which blanks for coining were punched, the result is more likely to be a streak of similar color range.

Understanding how copper spots form helps the knowledgeable collector appreciate that such spotting is a natural consequence of the coin-making process and not something to be alarmed about. Indeed, veteran numismatists appreciate the "originality" that such features impart to an old coin. Copper spots and streaks imply that a coin still has its "original skin," a term that is used widely within the coin business to describe pieces that have not been improperly cleaned and are thus natural in appearance. Typically, gold coins having original skin will show a fine layer of gentle haze in addition to whatever spotting is present. It may be that originality is an acquired taste that does not come quickly to the novice, but it is something that every buyer of gold coins should strive to understand and appreciate.

1927-S Saint Gaudens with original surfaces showing copper spots
This 1927-S Saint-Gaudens $20 shows a few small scattered copper spots on its obverse at about 6:30 and on the R in LIBERTY. A large spot has formed on the central reverse. Click on the image to enlarge.

The new collector of vintage gold coins, whose introduction to the coin field was through more modern pieces, such as the American Eagle and Canadian Maple Leaf bullion coins, is initially inclined to see copper spots in a negative light, simply because they are rarely seen on gold coins made more recently. While the American Eagle coins do have copper and silver as part of their composition and may develop copper spots in time, the American Buffalo coins and most foreign bullion pieces are of nearly pure gold and will not spot under normal circumstances. This unfamiliarity with copper spots and streaks should not be a reason to condemn them, as such coppery coloring is as natural to vintage gold coins as their mint luster.

The professional graders at NGC understand this relationship between a gold coin's alloy and copper spots, and they address spotting as they would any other phenomenon that occurs naturally to coins over the passing of decades. With their appreciation of an old coin's antique quality, they are not put off by spotting that has occurred as a natural consequence of age. In extreme cases of spotting, however, NGC's graders may lower a coin's grade downward if they believe that the spotting diminishes a coin's fitness for a higher grade. Therefore, the buyer of NGC-certified coins may be confident that any such decision has already been factored into the final grades assigned. Only rarely is copper spotting or streaking such an issue that it affects a coin's grade, and to the veteran collector of coins a few colorful blushes may be viewed as an asset. This positive aspect, too, is factored into the NGC grade assigned to each coin.

1920-S Saint Gaudens with original surfaces showing a large copper streak
Large copper colored streaks, like that shown at 2:00 on this 1920-S Saint-Gaudens $20, can result when impurities in the metal alloy are spread on a coin's surface during the planchet-forming process. Click on the image to enlarge.

In instances when spotting is extreme enough to impact a coin's grade, there is a solution. Professional conservation of a coin using proven techniques may selectively eliminate such spotting without losing the coin's original skin. This ability to address specific aspects of a coin's surface appearance without harming its overall eye appeal is a hallmark of Numismatic Conservation Services, LLC. Anyone can clean a coin improperly, destroying, perhaps forever, its antique charm. On the other hand, it takes a knowledgeable professional to distinguish negatives from positives and selectively treat the former in a manner that brings out a coin's greatest potential in both certified grade and aesthetic value. The motto of NCS could be borrowed from the Hippocratic Oath: "First, do no harm." That is, indeed, the mission of NCS, and it works in concert with NGC in a seamless operation to provide coin buyers with the maximum potential of their coins.

Yes, copper spots can be a bit distracting to someone first discovering vintage gold coins. To the real connoisseur, however, a vintage gold piece is its own animal, possessed of features and qualities that are unique. NGC recognizes these qualities, and it assigns the correct grade consistently, factoring into the equation such variables as strike, luster, surface marks and, yes, copper spots. So, when you see a beautiful, completely original gold graded by the experts at NGC, remember that the few blushes of coppery toning may be evidence of originality and a badge worn with pride.