Insidious Fingerprints

Posted by Skip Fazzari, Authentication Consultant to NGC, on 3/17/2008

Fingerprints are like a cancer to a coin, and can become irreparable if they are ignored for too long. Skip Fazzari describes the different types of fingerprints and what you can do to correct them.

For most of you, habit and experience have lessened the odds of marring the surface of your coins with fingerprints. You hold a coin properly — by its edges and close to a soft surface. Occasionally, there might be a lapse in this protocol but in most cases, we can assume that any fingerprints found on your coins resulted from carelessness or mishandling by non-collectors.

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It is difficult to know how long a fingerprint has been on a coin. Sometimes, especially in the case of Proof coins, they are easy to see the moment they occur; however, in most cases, fingerprints are not detected when they are fresh. Fingerprints are like a cancer to a coin. If ignored for too long, the chemicals in our body oils will actually etch the coinage metal. Over a period of time, and depending on their chemical makeup and the environment, they will “set” on a coin’s surface, making them difficult to remove. Copper and silver coins are the most likely to be permanently damaged in this way. Once this happens, the traces of fingerprints are virtually impossible to remove without abrasive cleaning that ruins more of the coin’s original surface. For the most part, gold is not susceptible to any type of permanent damage from fingerprints; however, on a few occasions, I have encountered a print pattern on gold that cannot be removed.

A “fresh” fingerprint is one that can be removed easily. A solution of soap and water will often restore the coin’s surface. Between the extremes of fresh prints and those that are etched into the surface are blemishes that may be removed with a mild acidic coin dip. The key to any form of treatment is to keep the coin’s surface as original as possible and free from any of the hairlines we associate with improper cleaning. As with all conservation efforts, these techniques are best performed by experienced and trained professionals

Two other types of “fingerprinting” come to mind. Occasionally, a “reverse print” can be seen on a coin. This occurs when grease deposited on the coin from our skin protects its surface from further contamination. The print only becomes apparent as the surrounding surface is toned. The other type of print occurs when the hazy patina or “skin” of a gold coin is marred by the shine of a greasy smudge or print due to mishandling.

Fingerprints that have become “set” can have a much larger effect on a coin’s grade than one might think. This is because they are very noticeable when they are fully developed and they detract so much from a coin’s eye appeal. Their size, color, and location combine to determine how much they will influence a grader. In many instances, the attempt to remove a fingerprint will make matters worse. Mature prints often appear as brown stains on red uncirculated copper and tan to dark brown stains on brown copper. If these coins are “dipped” in an effort to remove the fingerprint, the copper will turn pink and the coins will likely be rejected by the major grading services because of their artificial color. Therefore, this procedure is not recommended for copper coins. Fingerprints on silver coins usually range from gray to black. A darker stain usually indicates a deeper reaction. Dark prints on silver coins will turn gray when the coin is dipped.

This article previously featured in Numismatic News.