If you are visiting a gold jewellery or just doing some research on gold bars and coins, you cannot escape the term fineness of gold.
The precious metal is actually brittle and other metals have to be added to it to ensure that it remains strong. This is where the purity of gold changes.
Therefore, to measure the purity of gold the term fineness of gold is often used. Fineness of gold is always measures in 1000 parts. So, let's say the seller of gold bar says that the gold bar is of .995 purity.
Fineness is also known as Millesimal fineness and is indicated in 1000 parts of the whole weight. Gold coins have commonly a fineness of .999.
The purest form of gold that is currently produced is .999