Gold is denser than almost all other metals, hence hard to fake. A coin that is not gold or below the expected fineness will either be too light for its size or too large for its weight. Most metals of similar or higher density to gold are as expensive or more and were unknown in ancient times (notably the
platinum group). During the 19th century, platinum was cheaper than gold and was used for counterfeiting gold coins, though these coins could be detected by acoustic properties. Only two relatively inexpensive substances are of similar density to gold:
depleted uranium and
tungsten. Depleted uranium is government-regulated, but tungsten is more commonly available. and fairly easy to detect when comparing their weights, colors and sizes to authentic pieces. This is because the cost of reproducing a coin precisely can exceed the market value of the originals. However, since about 2015 counterfeit coins have been "flooding the market at an astonishing rate" and "it's gotten to the point where even people who deal with coins all the time may not be able to recognize a counterfeit coin right away" (
American Numismatic Association (ANA), 2016). The coins consist mostly of tungsten plated thinly with gold, have the correct weight, correct or near-correct dimensions, and are professionally produced in China. The weight and dimensions of a coin of .999 fineness such as the
Maple Leaf cannot be replicated precisely by a gold plated tungsten core, since tungsten has only 99.74% of the
specific gravity of gold. However, forgeries of alloyed gold coins (such as
American Gold Eagle or
Krugerrand made from a
crown gold alloy with 22 karats = .917 fineness) may have the correct weight and dimensions because of the lesser density of the alloy. Such forgeries can be detected by testing their acoustic, electric resistance or magnetic properties. The latter method uses the fact that gold is weakly
diamagnetic and tungsten is weakly
paramagnetic. The effect is weak so that testing requires strong
neodymium magnets and sensitive conditions (e.g. a gold coin hanging from 2 m long pendulum or placed on Styrofoam floating on water), but such tests can be performed without special equipment.
Pirates biting gold Biting a coin to determine whether it is genuine or counterfeit is a widespread cliché depicted in many films (like the 1917
The Immigrant), books (like the 1925 ''L'Or
by Blaise Cendrars) and plays (like the 1938 Mother Courage'' which is set in the
Thirty Years' War 1618–1648). According to a 2017 study, the
assumed widespread practice of pirates biting into a coin is almost certainly a Hollywood myth. The rationale for biting a coin was the supposed widespread dissemination of gold-plated lead coins in the 19th century: since lead is much softer than gold, biting the coins was an effective test. While fine gold is softer than alloyed gold, and galvanized lead is still softer, biting coins can only detect the crudest of forgeries. In addition, all "gold" coins minted for circulation in the UK and America since the
Tudor period (1485–1603) contained copper which made them more durable and thus hard to bite.
Numismatic fakes There are well made counterfeit gold coins in circulation. For example, the
St. Gaudens Double Eagle counterfeit, known as an
Omega counterfeit, is famous for its quality. Another example is the US$20 gold coin (
double eagle), which has raised lettering around its rim. If the coin is uncirculated, the letters will be flat on top. If slightly rounded, and the coin is uncirculated, it is a counterfeit. There are other counterfeit double eagles in which the gold and copper alloy was not thoroughly mixed, giving a slightly mottled appearance. ==See also==