There is some Truth in Television to this trope. Gold and silver coins were used for much of history, as were coins made of copper, bronze and other "cheap" metals to represent lesser values, and even modern day currencies often invoke this by making their highest denomination coins golden, their middle ones silvery, and their lowest ones copper or bronze.
Obviously, gold is more valuable than silver, which is itself more valuable than copper or bronze, but the value of individual coins depends as much on the weight and purity of the coin as it does on the value of the metal itself, though within the region that actually produced it, people were often forced to use overvalued coins — this is rarely reflected in fiction. Also rarely used is multiple denominations of coin made out of the same metal; a gold coin weighing twice as much as another gold coin would be worth twice the amount (assuming equal purity), but don't expect to see anything besides a generic "gold piece" ever mentioned in fiction.
The idea of a decimal exchange rate between different coins has absolutely no basis in fact — even if coins were minted to deliberately have this relationship, the price of metals varies, and the "exchange rate" between different coins would fluctuate with time just as exchange rates between currencies do.
Of course this is all moot if a governing body (either a bank or government) issues the coins; in real life in the modern world, coins and bills are made out of various materials whose value has nothing to do with the value of the currency (because the face value should always be significantly more than the melt value of the materials used to make it). Such modern coins and bills either have a fixed exchange rate for precious metals ("representative currency"), or have a value buoyed entirely by the faith and credit of the government ("fiat currency").
Real Life Examples:
- The ancient Romans used a system of gold, silver and copper coins and were the origin of this trope. Later European systems, such as the English pound, shilling, and penny, although they no longer used different metals, were inspired by the Roman system and based their value on the traditional exchange rates of gold to silver and silver to copper.
- British Pounds and Canadian dollars used to conform broadly to the colour scheme of this trope; the highest value coin is gold-coloured, smaller denominations are silvery and pennies are copper. Gold and silver were replaced by naval brass and a zinc alloy respectively decades ago, with the last holdout being pennies until demand for copper in electronics pushed the prices up; the British switched to electroplated stainless steel, while the Royal Canadian Mint switched to copper-plated zinc in 1997, stopped minting pennies in May 2012, and ceased distribution in February 2013. Both British
◊ and Canadian currency go on to subvert the trope with 2 dollar\pound coins that are combined gold and silver.- With the appearance of the Sacajawea and presidential dollar coins, the US conforms to these colors as well. Dollar coins have failed to catch on but they are very popular at renaissance fairs because of this trope, with prices sometimes listed in gold pieces.
- Before it went to a fiat currency system, the United States' currency was standardized around the copper penny, the silver dime, quarter, half dollar and dollar, and the gold eagle (worth ten dollars). There was also a half eagle, worth $5, and a double eagle, worth $20, and these latter coins were gold too.
- The coinage of Japan during the Tokugawa period actually used a system much like this with several, large denomination gold coins (generally oval, such as the Koban and even larger Oban), small rectangular coins that used an alloy of gold and silver, medium-sized rectangular coins made of silver with a fixed value relative to the gold coins, and finally several denominations of smaller copper or bronze coins (circular with a hole in the middle so they could be strung together for convenient transportation). During the economic crisis of the 1860s, the Shogunate government fixed the values of the coins at a 1:10 rate between the gold and the silver, enacting this trope nearly verbatim. Due to the mismatch between the "official" values and the actual market rates (which generally fluctuated between 1:15 and 1:18), foreign speculators took advantage of the cheap gold, exporting almost all of it out of Japan and causing disastrous effects to its economy.
- Croesus, King of Lydia, is credited to be the first person to mint true gold coins, as the previous coins were made of electrum (an alloy of silver and gold). After him, King Pheidon of Argos created the first real silver coinage.
- Traditional Hungarian currency followed the Au/Ag/Cu standard, and the names of the various coins were based on the sounds they made when struck on a hard surface:
- Gold – csengő, "clinking"
- Silver – pengő, "ringing"
- Copper – kongó, "pealing"
