Gold is used in so many things like industrial use, dental use or in making jewelry. These things usually determine the purity of base gold element. Carat represents purity of gold which means the higher carat the purer gold you have.In within processing gold it must be alloyed with other metals like copper or aluminum for durability and environmental resistance. For better understanding composition of alloys used in jewelry some standards are implemented on world level, system we all know as carat system.
24 carat is pure gold with no other metals inside. That means that 24 carat of gold have 99.9% of gold inside. There is almost impossible to get 100% purity of gold so 99.9% is taken as 24 carat instead.
Here is table of some common gold carat standards
22 carat is 916.6 fine gold metals. It means that 22 carat gold bullion has 91.66% gold inside.
18 carat is 750 fine gold metals. This represents gold bullion with 75% purity.
14 carat is 585 fine gold metals. This is alloy with 58.5% gold inside.
9 carat is 375 fine gold metals. Here we have 37.5 percent gold inside alloy.
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