For more than 6000 years gold has always been, and will probably always remain the metal par excellence with jewellers. Gold and jewellery, in fact, are almost synonymous in people's minds because of its ancient use for this purpose. This unique position of importance is not simply due to its rarity, but also its appearance, and the very character of the metal itself. Gold in its purest form has a unique bright yellow colour, which combined with its ability to take and retain a long lasting lustre, has given gold an ancient symbolic connection with the sun. It is chemically inactive when pure and almost incorruptible and will not oxidise in air. This quality, through time, gave gold a mystic significance and a symbolic association with the idea of immortality. Although gold in its purest state is too soft for practical use, it is easily alloyed with other metals. Such combinations, while giving it durability, allow it to retain its desirable qualities to a great extent. Alloying also causes gold to take on different colours, depending on the constituents of the alloy and their proportion to the gold. It is through the alloying of the metal, manufacturers have been able to produce different carats of gold, e.g. 9ct, 14ct, 18ct and 22ct.