From the green-gold coins used by the ancient Lydians in the ninth century B.C. to the red and gold décor and jewelry of the 14th century Chimu Empire in northern Peru, gold has always been a popular commodity. The modern market has standardized and formalized the classification of gold – if you've seen a piece of jewelry labeled with a number like 14, 18 or 24 then you may already be familiar with this system. These numbers refer to what are called 'carats,' and they serve as a guide to the purity of the gold you're buying.
Carat, Karat, or Carrot?
The words 'carrot' and 'carat' are often confused. Remember, a carrot (spelled with an 'o' for 'orange') is a delicious root vegetable that grows in the ground. But when talking about gold and gemstones, the correct words are carat or karat. It's said that the word 'carat' comes from the ancient Greek practice of weighing gold with carob beans – so maybe it all comes back to food after all!
'Carat' (abbreviated 'ct') is the original term that was used to describe both the weight of gold and gemstones and the purity of gold. The word 'karat' (abbreviated 'K') was later introduced to specifically describe the purity of gold. You may see the word 'carat' used interchangeably for both gemstone weight and gold purity in some countries (the United Kingdom and Australia often do this), but as for 'karat,' this only ever describes the purity of gold.
What Is an Alloy?
Pure gold is very soft, so it is rarely used on its own. Instead, other metals are added to gold to alter its durability, strength, color and price. This mixing of metals produces what's known as an alloy. Some common metals used in gold alloys are silver, nickel, copper, zinc and platinum. Silver is a popular component in gold alloys because it is tarnish-resistant, which helps keep it shiny and scratch-free.
Different alloys also determine whether gold is hypoallergenic or not. For example, like gold, silver is a hypoallergenic metal, so people are unlikely to have an allergic reaction from gold/silver alloys. However, low-carat golds (in the 9K or 10K range) often contain higher portions of potentially allergenic metals. Therefore, people who are allergic to certain metals should opt for high-carat gold. Additionally, some natural alloys, like cadmium, are toxic and cannot be used to make jewelry.
How Is Gold Purity Measured?
When describing gold purity, a parts system is used. Because it is difficult to get 100% gold, pure gold is an alloy of 99.9% gold and 0.1% other metals. This is termed in the industry as 24 out of 24 parts gold, abbreviated as 24ct or 24K, depending on the location. Therefore 18-carat gold is 18 out of 24 parts gold, or 75% gold and 25% other metals. Likewise, 14-carat gold is 14 out of 24 parts gold, with the remainder being other metals. In many countries, the lowest grade alloy that can still be classed as gold is 10-carat gold, which contains 58.3% alloys.
The Many Colors of Gold
There are many different colors of gold. While yellow, rose, white and green are the most common colors of gold, occasionally blue, purple and black gold are also made. It is the different alloy and gold mixtures that produce a wide range of colors. For example, yellow gold, or 'true' gold, is a blend of silver, copper and zinc. To create red or rose golds, the gold alloy includes copper. In blue gold, the metal added is iron, purple gold features aluminum, and black gold contains cobalt.
Gold alloys are either found naturally in the Earth's crust or blended manually by humans to achieve a particular result. For example, white gold was made to mimic the naturally white platinum's appearance, scratch resistance and hardness. Though white gold alloy is typically made of a gold and platinum mix, sometimes a blend of zinc, palladium and nickel is used to create the same effect.
The value of each gold color depends on its popularity at the time and the value of the metal alloys it's blended with. For example, 18ct rose gold is typically more affordable than 18ct yellow or white gold. This is because the copper in rose gold is considered a lower-cost metal than the silver or platinum found in yellow and white gold.
About the Author
Adrianne Elizabeth is a freelance writer and editor. She has a Bachelor of Science in Ecology and Biodiversity, and Marine Biology from Victoria University of Wellington in New Zealand. Driven by her love and fascination with all animals behavior and care, she also gained a Certificate in Captive Wild Animal Management from UNITEC in Auckland, New Zealand, with work experience at Wellington Zoo. Before becoming a freelance writer, Adrianne worked for many years as a Marine Aquaculture Research Technician with Plant & Food Research in New Zealand. Now Adrianne's freelance writing career focuses on helping people achieve happier, healthier lives by using scientifically proven health and wellness techniques. Adrianne is also focused on helping people better understand ecosystem functions, their importance, and how we can each help to look after them.