Pure gold is 24 karat, and it's too soft to use in jewelry - it would bend, dent, or break very easily. Fourteen, ten, and nine karat gold are all blends of alloys (metals other than gold) and pure gold.
The karat number indicates how much alloy metal has been added to the pure gold, using the full 24 karat as the starting point for measurement. Fourteen karat gold is, therefore, 14/24 gold and 10/24 alloy metal; likewise, ten karat is 10/24 gold and 14/24 alloy metal.
For yellow gold, the base metals used are silver, copper, and zinc.
"Rose" or "White" Gold?
The different colors of gold are achieved by blending different alloy metals with the pure 24 karat gold. Fourteen karat yellow gold - the gold most commonly used in gold jewelry - is made with fourteen parts of pure gold and ten parts of a combination of silver, copper, and zinc.
Rose gold uses more copper and less silver than yellow gold.
White gold uses nickel instead of silver.
And green gold - which is more commonly seen in antique jewelry - uses more silver and less copper than yellow gold.
Differences between Sterling Silver, 925 Silver and Fine Silver?
Silver needs to be combined with other metals because it is very soft, making it difficult to work with. Hardness has to be introduced, by adding other metals.
Sterling Silver consists of 92.5% silver and the remaining 7.5% consists of other metal, mostly copper. This is the reason why Sterling Silver is popularly referred to as 925 Sterling Silver or just 925 Silver.
The reason silver needs to be combined with other metals is that it is very soft, making it difficult to work with. A bit of hardness has to be introduced, by adding other metals.
Fine silver is 99.9% silver and has a small content of other metals such as copper.