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GOLD (YELLOW GOLD)
Gold is a chemical element with symbol Au and atomic number 79. In its purest form, it is a bright, slightly reddish yellow, dense, soft, malleable and ductile metal. Chemically, gold is a transition metal. It is one of the least reactive chemical elements, and is solid under standard conditions. The metal therefore occurs often in free native form, as nuggets or grains, in rocks, in veins and in alluvial deposits. It occurs in a solid solution series with the native element silver (as electrum) and also naturally alloyed with copper and palladium. Less commonly, it occurs in minerals as gold compounds, often with tellurium (gold tellurides).
Gold has been a valuable and highly sought-after precious metal for coinage, jewelry, and other arts since long before the beginning of recorded history. In the past, a gold standard was often implemented as a monetary policy within and between nations, but gold coins ceased to be minted as a circulating currency in the 1930s, and the world gold standard was finally abandoned for a fiat currency system after 1976. The historical value of gold was rooted in its medium rarity, easy handling and minting, easy smelting, corrosion resistance, distinct color, and non-reactivity to other elements.
Because of the softness of pure (24k) gold, it is usually alloyed with base metals for use in jewelry, altering its hardness and ductility, melting point, color and other properties. Alloys with lower karat rating, typically 22k, 18k, 14k or 10k, contain higher percentages of copper or other base metals or silver or palladium in the alloy. Copper is the most commonly used base metal, yielding a redder color.
Green gold is best described as yellow gold with a slightly greenish hint. Fourteen- and eighteen-karat gold alloys with silver alone appear greenish-yellow. Fourteen karat green gold would contain fourteen parts yellow gold and ten parts silver. Eighteen karat green gold would contain eighteen parts yellow gold and six parts silver.
White gold is an alloy of gold and at least one white metal, usually nickel, manganese or palladium. In order to make the gold white, it is combined with metal alloys that are white in nature and plated with an extremely hard element called rhodium. Although strong, rhodium may wear away over time. Replating is a simple process that can be done to restore whiteness to rhodium-plated jewelry. White gold alloys can be made with palladium or nickel. Alternative white gold alloys are available based on palladium, silver and other white metals, but the palladium alloys are more expensive than those using nickel. High-karat white gold alloys are far more resistant to corrosion than are either pure silver or sterling silver.
Rose gold is created by increasing the copper-colored alloys normally found in gold and decreasing the silver-colored alloys. 14K rose gold contains as much gold as 14K yellow gold but is slightly pinker in color. Rose gold is available in both 14K and in 18K. The 14K, rose gold has a more pronounced rose color.