It also safeguards responsible manufacturers by providing an independent assessment of quality and content that in which the public has confidence. The assay protects the consumer by ensuring sure that not too much base metal was used. Quite properly they must be alloyed with base metals (which happen to be cheap) for manufacturing. Precious metals such as old, silver, and platinum are too soft to use alone for making jewellery, cutlery and other goods. It is impossible to tell the precious metal content of any item simply by looking at it. This confidence is provided by an 'assay' (test and assess) of the precious metal content of that item. It is critical from the public's perspective that there is confidence in the claimed purity of any particular item made from precious metals. Gold is found in sea water, but no effective economic process has been designed (yet) to extract it from this source. Two thirds of the world's supply comes from South Africa, and 2/ 3 of USA production is from South Dakota and Nevada. It is found free in nature and associated with quartz, pyrite and other minerals. It is unaffected by air and most reagents. A mixture of one part nitric acid with three of hydrochloric acid is called aqua regia (because it dissolved gold, the King of Metals). The most common gold compounds are auric chloride (AuCl 3) and chlorauric acid (HAuCl 4). Gold is readily available commercially and its price changes day by day and is one of the most widely tracked commercial prices. It is a good conductor of heat and electricity, and is unaffected by air and most reagents. It is a soft metal and is usually alloyed to give it more strength. ![]() It is the most malleable and ductile metal 1 ounce (28 g) of gold can be beaten out to 300 square feet. It is metallic, with a yellow colour when in a mass, but when finely divided it may be black, ruby, or purple. It is estimated that all the gold in the world, so far refined, could be placed in a single cube 60 ft. Gold is usually alloyed in jewellery to give it more strength, and the term carat describes the amount of gold present (24 carats is pure gold). Remarkably other colours such as purple (a gold:aluminium alloy), blue (a gold:indium alloy) and even black (a gold:cobalt alloy) may be formed. Addition of some copper gives "rose gold", a soft pink colour. White gold is commonly used for wedding rings in the USA. White gold for jewellery is formed by mixing palladium, silver, or nickel with gold, although the result is green gold with certain proportions of silver. Small amounts of other metals alloyed with gold change the colour as well as mechanical properties such as hardness. The gold colour seems related to relativistic effects of the outermost gold orbitals. Most metals are metallic grey or silvery white whereas gold is characteristically a metallic yellow colour, in other words gold-coloured.
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