The noble metals
The noble metals are platinum, palladium, gold and silver. They are resistant to corrosion and oxidisation and are all rare and most are used for many other medical and industrial applications. There are two other metals, also commonly used by jewellers, that are not known as noble metals. Titanium – discovered in the 18th century in Cornwall and named after the Titans in Greek mythology. And Niobium, named after Niobe, also from Greek mythology, and used in the steel industry.
Gold and silver have been worked into fine jewellery, gifts and coins for over 6,000 years.
Gold: Gold is very malleable. It is mixed with other metals – usually silver and copper – to alter the colour, make it more resistant to scratching and reduce the price. The purity is measured in ‘carats’, pure gold being 24 carat gold; the term is thought to derive from the ancient Greek word, Keratia, which was 1/24th of the weight of the Byzantine gold coins. The Hallmarking Act in the UK applies minimum standards to 9 carat (375), 14 carat (585), 18 carat (750), 22 carat (950) and 24 carat which is 99.9% pure gold. The UK government has now introduced Nickel Act preventing the use of nickel and certain alloys in the production of gold as it is known to cause severe allergic reaction.
About half of all the gold that is mined today is used for jewellery, the remainder being used by industry and for investment – sometimes in the form of gold ingots or coins and sometimes in the form of shares.
It is said that most of the gold lies at the core of the Earth, deposited by meteorites as the planet was being formed. The mines are deep – up to 12, 000 feet in some areas and very hot – and the gold is found in tiny particle encased in hard rock, which is then extracted by use of a mixture of sodium, cyanide and zinc. The process has been further refined by a method using activated carbon called elution. However, since the 1970’s, much of the gold is recovered by use of gravity separation and the use of dangerous chemicals has declined.
Silver: There are two traditional British silver standards – Sterling silver which is 92.50% pure silver and Britannia silver which is 95.84% pure silver. More recently 800 silver at 80% pure silver was accepted in changes made to the Hallmarking Act . The UK has a long tradition for making silver cutlery and other useful objects which were in every day use in the homes of the Middle and upper classes. Today those simple objects are highly valued and our contemporary silversmiths are amongst the most respected in the world.
Silver is still used in the photographic industry and also in medicine – Hippocates (the father of modern medicine) declared that silver had healing properties which we now know are due to the ions and compounds of silver having a toxic effect on bacteria.
Platinum: The platinum group of metals includes platinum, palladium, iridium, rhodium and ruthenium, have been used for only two centuries. The name translated from the original Spanish means ‘little silver’. Platinum is the purist of the noble metals and also one of the rarest elements on Earth. It has a very high melting point and consequently is the most difficult metal for the jewellers to work but it is very durable and has a curious tensile quality which means that the setting for a diamond on a platinum ring can be both very fine and very very strong. When polished is a silvery grey colour and is often plated with rhodium to make it white.
Platinum has many industrial uses including the manufacture of catalytic converters and spark plugs for cars.
Image of fine gold ingots and bars from www.123RF Stock Photos