This stems back to ancient times in the Mediterranean /Middle East, when a carat became used as a measure of the purity of gold alloys (see next Question 5). The purity of gold is now measured also in terms of fineness, i.e parts per thousand. Thus 22 carat is 22/24th of 1000 parts = 916 fineness.

Originally, ancient Middle Eastern traders used a carat (called a karat in the USA and Germany) as a measure of mass (weight) based on the carob seed or bean.

Gold ore is either dug from the surface or blasted from underground rock. It is then taken to a mill, where the gold is separated from the surrounding rock. The separated gold is melted to make gold-rich bars called **Dore bars**. These bars are refined using the **Miller process**, which uses chlorine gas to reach about **99.5% purity**. If even higher purity or removal of other metals (like platinum) is needed, the gold is refined further using the **Wohlwill electrolytic process**, reaching **99.9% purity**. Any leftover rock (called **mine tailings**) that still contains small amounts of gold can be treated with **cyanide** to dissolve the remaining gold. The gold is then recovered using the **carbon-in-pulp** method, and finally melted and refined again.

Gold ore is rock that contains gold in small quantities. It must be mined and processed to extract the pure gold.

• Jewelry (about 50%)
• Investment (coins, bars)
• Electronics (conductors)
• Dentistry and medicine
• Aerospace (coatings and connectors)

Common tests include acid testing, magnet test, or density test — real gold is non-magnetic and denser than most metals.