Gold Carats Decoded: The Science of Purity

Why is some gold bright orange and soft enough to bite, while other gold is pale, hard, and resistant to scratches? The answer lies in the **Carat system** (often spelled 'Karat' in the US). It is the international standard for measuring the proportion of pure gold in an alloy.

The Math of Purity

The word "Carat" comes from the Carob seed, which was used in ancient times as a weight balance. The system is based on a total of **24 parts**.

• 24 Karat (24k): 24 out of 24 parts are gold. This is 99.9% pure ("Three Nines") or higher.
• 18 Karat (18k): 18 parts gold, 6 parts alloy. This is 75% pure gold.
• 14 Karat (14k): 14 parts gold, 10 parts alloy. This is 58.3% pure gold.
• 9 Karat (9k): 9 parts gold, 15 parts alloy. This is 37.5% pure gold.

Why Alloy it at All?

Pure 24k gold is **exceptionally soft**. If you wore a 24k wedding ring every day, it would warp, dent, and eventually wear down to nothing. To make gold practical for jewelry, we mix it with "hard" metals like copper, silver, zinc, and palladium.

The Color Alchemy

By changing the metals we mix with gold, we change its color.

• Yellow Gold: mixed with silver, copper, and zinc. This is the traditional "classic" look.
• Rose Gold: mixed with a higher percentage of copper. The more copper, the redder the gold.
• White Gold: mixed with palladium or nickel. It is usually plated in **Rhodium** to give it that brilliant silver shine.

Look for the Hallmark

Legally, nearly every gold item must be stamped with a "Hallmark" indicating its purity. In Europe and the UK, this is often a three-digit number representing the parts per 1,000:

• 375 = 9k
• 585 = 14k
• 750 = 18k
• 916 = 22k
• 999 = 24k