How Coin Auctioneers Spot Fakes Before Sale
Coin forgeries and altered coins are entering the market. For the good of buyer and seller alike it is important that these are detected before the sale. This article outlines the steps a coin specialist takes in order to verify a coin before it is put up for auction.
Weight and Diameter Checks
All coins were minted to precise specifications and these are well recorded in reference works for most issuers. By weighing a coin and checking its diameter against published parameters for comparable coins the first potential indicators of a fake can be quickly identified. Note that even a difference of 0.5 grams can be significant enough to prompt further investigation.
Surface Examination Under Raking Light
Investigation under raking light can also reveal tooling, artificial wear and re-engraved high points to enhance grade. Circulation wear on genuine coins is uniform on the high points of the coin, uneven surfaces are suspect and show fine scratches running in the wrong direction.
Loupe and Microscope Work
A good 10x loupe can often detect signs of casting around the edge of a coin as well as a very rough surface with a granular texture of sand from a sand cast coin. Often a microscope is required to determine if a coin is real or not. Under magnification the die impressions can be compared to known die cracks and the exact punch alignment.
Metal Composition Testing
X-ray fluorescence analysis, or XRF, is a non-destructive test that determines a coin’s alloy composition. A silver denarius that tests as modern base metal, for example, is not a denarius, regardless of how it may have been refinished to resemble one.
Edge Inspection
Cast fakes will typically have a seam where the two halves of the cast have joined. Some altered dates will also have tool marks near the date figures. Running your thumbnail lightly around the edge of a coin can sometimes reveal raised lines or other marks that look perfectly normal when viewed from the front but are apparent when running your thumbnail around the edge of the coin.
Provenance and Die-Pairing Records
The coin can be matched to a recorded die pair or it has a published history of previous sales through auction catalogues. A coin that appears on the market for sale with no history of previous sales through auction catalogues and no published parallels is suspicious, regardless of appearance.
Understanding these checks will help you ask the right questions when buying a coin or having one consigned for sale.