What is a gold carat?
The gold carat is the international unit of measurement used to indicate the purity of the precious metal in a piece of jewelry. Unlike the carat for diamonds, which measures their weight, the gold carat expresses the proportion of pure gold contained in the overall alloy of the piece.
Where does the word carat come from and what is its origin?
The history of the word "carat" begins with the carob tree, a Mediterranean tree. In ancient trade, the small seeds contained in its pods, considered sufficiently regular in weight, were used as counterweights to weigh stones and other precious materials. This practice has left its mark on vocabulary. The Greek kerátion, which referred to carob but also a small weight, became qīrāṭ in Arabic, then carato in Italian and finally carat in French.
Later, the carat also became a measure of gold purity. In monetary systems inherited from antiquity, particularly around the Roman and then Byzantine solidus, gold was progressively evaluated on a 24-part basis: 24-carat gold was thus considered pure. Today, in English, karat generally refers to the purity of gold, while carat measures the weight of precious stones. In French, "carat" is used in both senses.
How is gold purity understood in 24 parts?
The purity of a gold jewel is traditionally expressed in carats, on a scale of 24 parts. 24-carat gold thus corresponds to what is considered pure gold. A 14-carat gold jewel contains 14 parts of gold out of 24, with the remaining 10 parts consisting of other metals added to modify its hardness, color, or resistance. The designations 10K, 14K, and 18K are commonly found in North America, particularly in Quebec, where the carat remains the most familiar reference for describing the gold content of a jewel.
The impact of alloys on color and physical properties
As pure gold (24 carats) is too malleable and soft to withstand daily shocks, the addition of other metals is essential. This choice of alloy radically changes the characteristics of the jewelry. To better understand, 18K gold corresponds to 75% pure gold, 14K gold corresponds to 58.5% pure gold, and 10K gold corresponds to 41.7% pure gold.
- Cultural variations and resistance: Quebec and the North American market heavily favor 14K and 10K gold for their excellent daily durability and accessibility, as the integration of hard metals (copper, zinc, silver) makes the structure more robust against scratches. Conversely, Europe remains historically attached to the prestige of 18K gold, while in Asia, a store of value is sought with 22K or 24K gold, which is very yellow and malleable.
- The case of white gold: To obtain white gold, natural yellow gold is mixed with whiter metals, such as palladium, silver, or, depending on the alloys, nickel, copper, and zinc. These metals reduce the yellow color of gold while modifying its hardness and resistance. Nickel has long been used to produce a more pronounced white, but its use is now strictly regulated in some regions due to the risk of allergies. Finally, many white gold jewelry pieces receive a rhodium plating, which gives them their characteristic bright white luster.
- The case of rose gold: To obtain this warm and romantic hue, natural yellow gold is mixed with a high proportion of copper, often supplemented with a hint of silver. Beyond its distinctive color, the strong presence of copper profoundly transforms the physical properties of the jewelry: it makes rose gold significantly harder and more scratch-resistant than white gold or traditional yellow gold of the same carat. Unlike white gold, rose gold does not require rhodium plating, which means that its color is entirely natural and will never fade with age. A 10K alloy will offer a more intense pink hue and increased robustness, while an 18K alloy will present a softer and more subtle pink due to its higher fine gold content.
Our jewelers' advice
Choosing the right karat is about finding the balance between the richness of the gold, the durability of the jewelry, and your budget. 18K charms with its high gold content and deep color, while 14K offers a good balance of elegance, durability, and affordability. 10K is also a good option for everyday jewelry, especially when you want to keep it more accessible despite the price of gold. And in white gold, the visual difference between karats is very subtle, particularly when the jewelry is rhodium-plated.
Frequently asked questions about the gold carat
14K gold contains a higher proportion of structural metals. This composition significantly strengthens the jewelry, allowing for the creation of more durable settings and ensuring that the prongs securely protect the stone from everyday impacts.
Basic white gold retains a very slight warm yellow hue beneath its surface. With friction and over the years, the thin layer of rhodium that gives it its dazzling whiteness eventually fades, revealing the true color of the underlying alloy, which requires a new rhodium plating in the workshop.
If your jewelry comes from Europe, you will not necessarily see the inscription 10K, 14K or 18K, but rather a three-digit number corresponding to the millesimal fineness system. A 750 hallmark means that the jewelry contains 750 parts of pure gold out of 1000, which is the equivalent of 18 carats. The number 585 corresponds to 14 carats, while 417 indicates 10 carat gold.