More on Cast Counterfeits

Posted by Skip Fazzari, Authentication Consultant to NGC, on 12/12/2007

Skip Fazzari uses an example coin to illustrate how to detect cast counterfeits.

click image to enlarge

This month, I’m going to continue writing on the topic of cast fakes. Since a picture is worth a thousand words, I’ll use a micrograph to illustrate some of the flaws to look for on the surface of a casting. The counterfeit I’ll use is not a very deceptive example; however, a genuine coin with a corroded surface may appear similar.

Last time I wrote about making a mold from a genuine coin. During this step, if any tiny air bubbles become trapped between the coin and the mold material, they may be impressed into the mold, causing a round depression in its surface. At the same time, the bubble will prevent the mold material from touching the surface contour of the model and cause a defect in the mold. Then, at the time material is poured into the mold to form the cast piece, it will fill the hole left by the air bubble. This will leave a raised, round lump on the surface of the fake like the tiny lump seen in the claw of the eagle.

Additionally, if any air bubbles are present in the metal going into the mold, they may work their way to the surface of the casting as it is cooling. These bubbles will prevent metal from filling in the design of the mold. At the place where this occurs, a round depression will be seen on the surface. Take a look at the shallow crater just above the “O” in Dollar and in line with the claw. Look closely as the depression blends into the surface. The dark hole above the claw is from damage. One way to differentiate damage and raised corrosion defects from casting depressions and pimples is to note the quality of the surface. Casting defects should have a similar surface as the rest of the cast — they blend in. Damage usually has a different color from the surface unless the coin is cleaned or toned.

Study the field of this cast closely and you will see hundreds and hundreds of microscopic craters. This is what gives some casts their “granular” look. One last thing, the micrograph was taken at ten power using a fluorescent bulb to show the coin’s surface in an even light. It would be hard to duplicate this view using just one eye and a magnifying glass unless the examination is made by an experienced numismatist.