Aluminium was once too precious for anyone but Napoleon III's favourite guests
At a banquet thrown by Napoleon III, the most honoured guests ate with aluminium cutlery while lesser visitors made do with silver. The metal was so hard to extract that it outranked gold. What makes a metal precious, it turns out, is less its chemistry than how scarce it is.
Precious metals are rare, naturally occurring metals of high value. Most resist corrosion, react little with other substances and have a bright lustre. Gold and silver are the classic coinage metals, prized for art, jewellery and money, and the platinum group adds ruthenium, rhodium, palladium, osmium, iridium and platinum, with platinum the most widely traded. Gold, silver, platinum and palladium even have their own ISO currency codes.
Rarity is the whole game. A new ore discovery or a better refining process can knock a metal off its pedestal, as aluminium learned. It is the most abundant metal in Earth's crust, but separating it from its ores was once so costly that bars of it were displayed at the Paris Exposition Universelle of 1855. Once cheaper extraction arrived, it became an everyday material by the late 1800s.
Metal traded in bulk is called bullion, valued by weight and purity rather than any face value. Three nines, or 99.9% purity, is common, and Canada's Gold Maple Leaf reaches 99.999%; perfect purity is practically impossible because each further step gets harder. Many countries issue bullion coins as nominal legal tender, though their metal is worth far more than the figure stamped on them. In 2012 the Perth Mint struck a one-tonne gold coin with a face value of one million Australian dollars, the largest minted coin in the world.
Today these metals serve mainly as investments and industrial materials. Investors see gold and silver as a hedge against inflation and downturns and watch the gold-to-silver ratio, one of the oldest continuously tracked price relationships. Platinum and palladium are crucial catalysts in car exhaust converters, while gold and silver nanoparticles appear in biosensors and solar cells.
Source: Precious metal
