Gold Coin - Counterfeits

Counterfeits

For most of history, coins were valued based on the precious metal they contain. Whether or not a coin was actually made by the party as claimed was of secondary importance compared to whether or not it contains the correct amount of metal - that is, correct weight and fineness (purity). Genuine appearance was simply a convenient shortcut to avoid time-consuming tests in everyday transactions.

Unlike silver, gold is denser than almost all other metals, hence whether something is made of gold is extremely hard to fake. Simple determination of weight and volume should be sufficient. A coin that is the right size but is not gold, or has too much base metal, will be "light"; alternately, a coin that weighs right will be somewhat larger. Most metals that are of similar or higher density than gold are similarly or more expensive, and were unknown in ancient times (notably the platinum group); only two relatively inexpensive substances are of similar density to gold: depleted uranium and tungsten. Of these, depleted uranium is government-regulated, but tungsten is more commonly available, hence more suited for counterfeiting. Alloying gold with tungsten would not work for several reasons but a coin with a tungsten center and gold all around it could not be detected as counterfeit by density measurement alone. This method (tungsten wrapped in gold) has found some use in counterfeiting of gold bars.

An old practice to test whether a gold coin was counterfeit was to bite down on it. Since pure gold is relatively soft any base metals mixed with the gold to lessen its value will also harden the coin, and so make it harder to bite on. Another explanation of this practice is that historic gold coins were usually alloyed with silver and copper which make them harder than pure gold and less prone to wear. Counterfeits could be made of lead to approximate the weight of gold and covered with a thin layer of real gold. Biting the coin would mark the softer lead or scratch through the veneer revealing the base metal underneath.

The majority of bullion counterfeits (of all types) are rare, and fairly easy to detect when comparing their weights, colors and sizes to authentic pieces. This is because the cost of reproducing any given coin precisely can easily exceed the market value of the originals.