Features of modern coinage

The milled, or reeded, edges still found on many coins (always those that were once made of gold or silver, even if not so now) were originally designed to show that none of the valuable metal had been shaved off the coin. Prior to the use of milled edges, circulating coins commonly suffered from "shaving", by which unscrupulous persons would shave a small amount of precious metal from the edge. Unmilled British sterling silver coins were known to be shaved to almost half of their minted weight. This form of debasement in Tudor England was commented on by Sir Thomas Gresham, whose name was later attached to Gresham's Law. The monarch would have to periodically recall circulating coins, paying only bullion value of the silver, and reminting them. Traditionally, the side of a coin carrying a bust of a monarch or other authority, or a national emblem, is called the obverse, or colloquially, heads. The other side is called the reverse, or colloquially, tails. However, the rule is violated in some cases.[13] Another rule is that the side carrying the year of minting is the obverse, although some Chinese coins, most Canadian coins, the pre-2008 British 20p coin, and all Japanese coins, are exceptions. In cases where a correctly oriented coin is flipped vertically to show the other side correctly oriented, the coin is said to have coin orientation. In cases where a coin is flipped horizontally to show the other side, it is said to have medallic orientation. The latter is found in British coins. Bi-metallic coins are sometimes used for higher values and for commemorative purposes. In the 1990s, France used a tri-metallic coin. Common circulating examples include the €1, €2, British £2 and Canadian $2. The exergue is the space on a coin beneath the main design, often used to show the coin's date, although it is sometimes left blank or containing a mint mark, privy mark, or some other decorative or informative design feature. Many coins do not have an exergue at all, especially those with few or no legends, such as the Victorian bun penny. Not all coins are round. The Australian 50 cent coin, for example, has twelve flat sides. A twist on it is wavy edges, found in the two dollar and the twenty cent coins of Hong Kong and the 10 cent coins of Bahamas. Some other coins, like the British Fifty Pence coin, have an odd number of sides, with the edges rounded off. This way the coin has a constant diameter, recosgnisable by vending machines whichever direction it is inserted. The triangular coin (produced to commemorate the 2007/2008 Tutankhamun exhibition at the The O2 Arena) was commissioned by the Isle of Man, became legal tender on 6 December 2007.[14] and has a value of 25p (a crown). Other triangular coins issued earlier include: Cabinda coin, Bermuda coin, 2 Dollar Cook Islands 1992 triangular coin, Uganda Millennium Coin and Polish Sterling-Silver 10-Zloty Coin.[15] Guitar-shaped coins were once issued in Somalia, Poland once issued a fan-shaped 10 złoty coin, but perhaps the oddest coin ever was the 2002 $10 coin from Nauru, a Europe-shaped coin.[16] Some coins, called bracteates, are so thin they can be struck on only one side. The Royal Canadian Mint is now able to produce holographic-effect gold and silver coinage. For a list of many pure metallic elements and their alloys which have used in actual circulation coins and for trial experiments, see coinage metals.[17] Coins are popularly used as a sort of two-sided die; in order to choose between two options with a random possibility, one choice will be labeled "heads" and the other "tails", and a coin will be flipped or "tossed" to see whether the heads or tails side comes up on top. See Bernoulli trial; a fair coin is defined to have the probability of heads (in the parlance of Bernoulli trials, a "success") of exactly 0.5. A widely publicized example of an asymmetrical coin which will not produce "fair" results in a flip is the Belgian one euro coin[18]. See also coin flipping. Coins are sometimes falsified to make one side weigh more, in order to simulate a fair type of coin which is actually not fair. Such a coin is said to be "weighted".