Mint error coins have long held a fascination for rare coin collectors. These are coins which were printed incorrectly at the mint and escaped detection during the mint’s screening process. Although an embarrassing oversight for the mint, these coins delight collectors for their novelty and scarcity. To put things in perspective, the U.S. Mint produces about 15 billion coins a year, of which roughly 50,000 are error coins.
To get an idea of the types of minting errors that can take place, it is necessary to have a brief understanding of how coins are produced. For starters, a mint purchases thin sheets of metal which are fed through a machine that punches out blank disks known as “planchets.” A typical error at this stage can be attributed to incomplete stamping so that a coin is produced with a portion missing. This coin is referred to as a “clipped planchet.”
Further errors can occur when the coin is struck. A specialized tool known as a die is used to create the image on the coin. It is basically a steel rod with a relief image of the design on it. If the die is damaged in some way (chipped or cracked), the image printed on the coin will be imperfect. Coins with these types of errors are called “die cracks,” “die breaks” or “double dies”.
Additional errors can occur in the manufacturing process if the coin is mis-fed into the coin press; if the coin gets stuck; if there is debris in the way; or if it bounces around on the production line. Collectively, these problems produce what are known as “strike errors” and are the most highly prized error coins due to their rarity. Error coins in this category include “broadstrikes,” “doublestrikes,” or “off-centre strikes.”
The value of error coins can vary significantly depending on the type of error produced, how scare it is, how significant the error is, the date, and the denomination of the coin. Depending on its rarity, an error coin can sell for thousands, if not millions, of dollars. A case in point is the interesting story of the 1899 Single 9, South Africa’s most famous and unique rare gold coin.
In 1899, during the Anglo-Boer war, a shipment of dies was intercepted by British soldiers. The dies were intended to create a new currency for the South African republic to legitimize its existence. Without the new dies, the government opted to re-use those from 1898 and stamp a 9 on the reverse of the 1898-dated coins. Once the first coin was stamped, they realized that the 9 was too large as it intruded onto the bust of President Kruger. Subsequently, two smaller 9s were stamped on the remaining coins. These coins became known as the ’99 Overstamp. The Single 9, as the first coin came to be known, passed through many hands until it was reportedly sold for an amount just over ZAR20 million ($2.4 million), making it one of the top five most expensive coins in the world.
A discussion of error coins would not be complete without a mention of mules. A mule is a coin that has two sides intended for different coins. These coins are extremely rare to find and can fetch prices of up to $75,000. A recent example is the Sacagawea Dollar/Washington State Quarter mule, which features a Statehood quarter on the front and the Sacagawea dollar on the reverse. Although several thousand were made in 2000, the mint destroyed nearly all of them. At present, only 11 remaining coins have been found to exist.