It is considered the most important among the noble metals, and it is a chemical element marked by the symbol Au. It is very ductile and malleable, it is resistant to chemicals and atmospheric agents and it has an intensive yellow colour in nature.
It has always been used as a parameter for every kind of valuable item, for the minting of coins and for precious items. Gold is listed per gram or ounce. Because of its extreme malleability, it is not manufactured by itself but it is combined with other metals that make it more resistant.
Depending on the quantity of gold, there are different types of alloys, in which gold is measured in thousandths. For example if we have a gold item that weighs 10,0 g with a gold concentration of 750 thousandths it means that there are 7,5 g of pure gold (999,9/1000) and 2,5 g of other metals. They are precisely these 2,5 g of other metals that determine the colour of the alloy. For example, with 2 g of silver and 0,5 g of copper, the final colour will be pale yellow. On the contrary, with 2 g of copper and 0,5 of silver, the final colour will be a red gold.
In order to obtain white gold, white metals will need to be added, like palladium, that, unlike nickel, is non-allergenic. The gold concentration, expressed in thousandths, must be present on every item with a weight above 1 g, next to the manufacturer’s brand that, in so doing, takes responsibility for the gold concentration declared on the item.
On the Italian market you can almost exclusively find items with a gold concentration of 750 thousandths, which is also obsoletely called 18 ct gold.
Here you can find a chart with the most common alloys and the respective worth in carats: