Gold - The Wonder Metal

Over the centuries, gold has played a unique cultural role in societies across the world. Something about the metal gives it a transcendent symbolic value: from the legendary treasuries of the Aztec and Mayan empires to the Golden Calf of the Book of Exodus, gold is implicated in the most dramatic tales of ancient human history. Even today, gold retains its cultural significance. For an Olympic athlete, a single gold medal represents the zenith of achievement. The Palme d'Or, or Golden Palm, is a symbol of supreme attainment in the film industry. Only a handful of British monarchs have managed to stick it out for half a century and earn their Golden Jubilee. And clearly there is a reason why credit card companies designate their high-end offerings as "Gold Cards". But what is it about real gold that captures our attention? What gives this yellow metal such value?
Like anything of real value, gold is rare. Only 3 particles per billion in the Earth's crust are gold. Although the world's oceans hold vast amounts of gold, it is so dilute that attempts to recover it from the salt water have never been successful. If all the gold ever refined were formed into a ball, it would be less than 25 metres across. However, some gold does exist naturally in a relatively pure state (as opposed to in an ore), enabling humans to gather it in small quantities without the need for chemical extraction. And once harvested, gold is one of the most versatile metals on earth. It has been crafted and shaped ever since the 'caltholithic', or 'copper' age, as early as 4000 BC, making it one of the very first metals to be used by humans. The ancient peoples of Egypt and the Middle East used gold for religious rites, as well as for ornamentation. The first recorded use of gold coins was during the reign of King Croesus of Lydia around 600 BC. Gold is also more malleable and ductile than any other metal. A single gram of gold can be beaten into a sheet one metre square. It is one of the heaviest elements; heavier, even, than lead. Ten teaspoons of gold would weigh as much as seventeen teaspoons of lead.
It has been customary throughout history to test the purity of gold by biting on it. Since pure gold is soft enough to show teeth-marks, and cheaper alloying metals are usually harder, this method does give some indication. More reliable tests, however, involve the use of nitric acid. The content of gold in alloys is measured in karats (k). Pure gold is 24 karat, with the number of karats decreasing proportionally as other metal is added.
Although too soft for ordinary use in its pure state, gold can be extremely hard and durable when alloyed with other metals. Alloying also has other advantages besides increasing its hardness. The distinctive yellow colour of gold is recognised throughout the world. However, a fascinating spectrum of other colours can be created by combining small quantities of other metals with the gold. Alloyed with copper, it has a rosy colour, with nickel, silver, or palladium it is white, with iron, blue, and with aluminium, a purple hue. Pure silver gives the alloy a greenish tint, and rhodium or ruthenium produce black. Gold in such forms is most commonly used in jewellery. "Colloidal" gold is micro-particles of gold suspended in water, producing an intense red colour. Colloidal gold is used in stained glass, and in certain applications for medical and scientific research.
In former years gold played an important role as a medium of exchange, mostly in the form of valuable coins. Currencies were also backed by gold, but this is no longer the case. Reserves of gold are still held by some nations as gold bullion coins, for example the Australian Gold Nugget, or the British Britannia. The value of these coins is measured by their weight, rather than by their face value, which, when it exists, is always significantly less than its true value. The world's biggest gold coin was minted by the Canadian Royal Mint in Spring 2007. It is half a metre across, 3cm thick, weighs 100kg, and is worth nearly 3 million dollars, with a face value of $1,000,000.
These days, most gold is used in jewellery, but it is also widely used by other industries. Dentists use gold alloys in crowns and bridges, and certain types of toners in the photography industry contain gold. Even the food industry uses gold flakes or dust to enhance the appearance of exotic sweets and drinks. Gold can be made into thread for embroidery, and beaten into micro-thin sheets called 'gold leaf'. More durable than any paint, the real gold never fades or loses its lustre. In fact, there are examples of gilding done by the Romans and Ancient Egyptians which still retain their brilliance today, thousands of years on.