Paladium
You can find yellow gold in 14 karat, 18 karat and 24 karat. The purest form of gold is 24 karat, but you seldom see it in rings because it is too soft for setting a diamond; 14 karat and 18 karat are used most often.When we talk about 14 karat gold, we refer to an alloy (a mix of metals) of 14 parts gold and ten parts other metal. Eighteen karat gold is an alloy of 18 parts gold and six parts other metal, and so on. The more "other metal," the stronger the gold. White gold doesn’t exist in nature. It is an alloy of yellow gold and a mixture of nickel, palladium, rhodium, and other metals, which turns the yellow gold to white.
In jewelry platinum is mixed with other metals to form an alloy, which means a compound of two or more metals. Typically this includes ruthenium, iridium, palladium, rhodium, copper, osmium or titanium. So when used for jewelry, such as wedding bands and engagement rings, platinum will always contain a certain amount of other metal alloys.
Because of the high melting point, and the other difficulties in extraction and refining, platinum is expensive to buy and process. This includes higher labor costs for manufacturing it, and also higher expense in recycling it.
In the jewelry industry, mixing precious metals with other, often less valuable, materials allows manufacturers to change the metal’s appearance, make it easier to work with, or reduce cost.