How Coins Are Made
A coin is a piece of metal stamped and issued by an authority for use as money. It is also used figuratively to mean something of value, especially a token used as evidence that an agreement has been made. The phrase “the other side of the coin” is an idiom referring to the fact that there is another way to look at an issue.
The term coin can also be used to refer to a single unit of a cryptocurrency that functions independently of other coins. Cryptocurrencies function through blockchains that monitor all transactions and make double-spending impossible. Coins can be minted by running computationally intensive algorithms called mining, or they may be purchased from others and then stored as an asset on the blockchain.
Most coins are made of a mixture of pure metals that must be accurately weighed and combined to produce the desired alloy. Pennies, for example, are composed of copper, zinc, and nickel. Higher-denomination coins are usually made of an alloy of 75 percent copper and 25 percent nickel, a mix known as cupronickel. The alloys are melted in electric furnaces and poured into molds to form ingots. These ingots are rolled down into strips that are the exact thickness required for each denomination of coin. The blanks are then fed into machines that cut circular, plain-surfaced disks, or coins, of the appropriate size.
After cutting the coins, a machine mills raised edges into them to prevent their surfaces from wearing away too quickly. The blanks are then put into a die, which strikes them under heavy pressure–ranging from 40 tons to 175 tons–to stamp the designs and other information on them. The design on the front of a coin is called the obverse, and the back, or reverse, is sometimes decorated as well. The year of minting is shown on the obverse, and most coins display the name of the country of issue on the reverse.
In the Middle Ages, each local authority–kings, princes, dukes, bishops, free cities, and even individual merchants–ran their own mints. This produced a wide variety of coinage, which often made successful trade between nations difficult. As nation-states gained control of Europe in the 13th century, they centralized their coin production and standardized the values of their coins.
Most coins are round, but they can be made in a variety of other shapes. Some have flat sides, such as the Australian 50-cent coin, and some have wavy edges, like the Bahamas 20-cent coin and Hong Kong $2 coin. The edge of a coin can be embellished as well, with a privy mark or other decorative feature. If a coin is kept in good condition, it can retain its value as a collector’s item or investment. However, rubbing and polishing can reduce the value of the coin by removing its surface along with the dirt and tarnish.