Since gold and silver are naturally soft and pliable, they are combined with other metals to make them harder. The additional metal alloys—copper, silver, zinc, nickel, palladium, and others—that are combined with the gold and silver are referred to as "additives."
The purity level of precious metal alloys is the proportion of the precious metal in the mass of the alloy. One thousandths are used to quantify purity. A "4 nines" alloy is one that is 99.99 percent pure. The price of the alloy is also influenced by the purity level.
Purity of Gold
The purity of the gold is expressed in karats, with one karat equaling 4.1666% of the total.
Israel allows the following standards of gold purity in trade:
Because 24 carat gold is 99.99% pure (4.1666 x 24 = 99.99),
hence, four nines excellent.
91.6% pure gold (4.1666 x 22 = 91.6%) and 8.4% additional metals are present in 22 carat gold.
87.5% pure gold (4.1666 x 21 = 87.5%) and 12.5% additional metals are present in 21 carat gold.
75% pure 18 karat gold.
58.5% pure 14-karat gold.
37.5% pure 9 carat gold.
According to Israeli legislation, goods with a gold purity of less than 9 karats are not regarded as gold goods.
The colour of the pure gold is determined by the other metals it is combined with. Pure gold (24 carat) is yellow; to keep it that way, palladium, copper, and silver are combined with it. Reddish-tinted copper is mixed with to produce "red gold," whereas paler metals like nickel or platinum are used with to produce "white gold".