Since gold is a very soft metal, it is typically alloyed with other metals. Pure gold, also known as fine gold, is not suitable for jewelry production as it is prone to scratching and bending.
To compensate for this negative property and achieve greater strength, other metals like silver, copper, palladium, etc., are mixed with pure gold. This process also creates different shades of gold, such as white or rose gold.
The challenge in creating the "ideal" gold alloy lies in finding a balance where the gold content is low enough to achieve the required strength, but not so low that the negative properties of the other alloy components outweigh the benefits. A higher proportion of other metals in the alloy can make the jewelry more reactive, leading to tarnishing and discoloration due to environmental factors.
Ideally, the gold content should range between 14 and 18 karats. Unlike gemstones, where a carat corresponds to a weight of 0.2 grams, when it comes to gold, karats indicate the gold content in the alloy as a fraction of 24.
So, 24 karat gold corresponds to 100 percent gold content, 18k is 75 percent, and 14k is 58.5 percent. Another way to indicate the purity of an alloy is through thousandths. For example, 18k gold is the same as 750 gold (750/1000), and 14k is 585 gold (585/1000).
For jewelry that would quickly tarnish due to the properties of its alloy, there is the option of electroplating. This involves chemically treating the metal and coating it with a thin layer (such as rhodium) that does not react.