Gold, a chemical element denoted by the symbol Au and atomic number 79, has captivated humanity for millennia due to its unique properties. In its pure form, gold is a soft, dense, and brightly colored metal. However, its inherent malleability means pure gold is often too soft for many practical applications, particularly in jewelry. To overcome this, gold is frequently combined with other metals, a process known as alloying. Alloying creates various forms of gold, each with distinct characteristics influenced by its composition and processing.
Understanding Gold Purity
The purity of gold is measured using the karat system, which indicates the proportion of pure gold within an alloy. The system divides gold into 24 parts, meaning 24 karat (24K) gold is 100% pure. While 24K gold is the purest, it is exceptionally soft and prone to scratching and bending, making it unsuitable for daily wear in jewelry. It is more commonly used in gold bars, coins, and some electronic or medical applications.
Lower karat numbers signify a reduced gold content and an increased proportion of other metals. For instance, 18K gold contains 18 parts gold and 6 parts alloy (75% pure gold). This offers a balance between gold content and durability, making it a common choice for high-quality jewelry.
14K gold is 14 parts gold and 10 parts alloy (58.3% pure gold). This karat is popular for its blend of durability, affordability, and attractive appearance, often used for engagement rings and everyday wear. The lowest common karat for jewelry in many regions, including the United States, is 10K gold (10 parts gold, 14 parts alloy, or 41.7% pure gold). Its higher alloy content makes it the most durable and affordable, though its color is paler due to less gold.
The Spectrum of Gold Colors
While pure gold is bright yellow, alloying allows for a wide array of gold hues beyond traditional yellow. These colors are achieved by mixing pure gold with specific ratios of different metals. The added metals not only enhance durability but also chemically alter the gold’s natural color.
White gold is created by alloying pure gold with white metals such as palladium, nickel, or silver. Although the resulting alloy may have a slight yellowish or grayish tint, white gold jewelry is commonly plated with a thin layer of rhodium to achieve its lustrous white finish. Rose gold, known for its warm, reddish-pink hue, is produced by alloying gold with copper, sometimes with a small amount of silver. The higher the copper content, the more pronounced the red tone becomes. Green gold, a less common color, is formed by combining gold with silver, and sometimes copper and zinc, which impart a subtle greenish tint.
Gold Beyond Solid
Beyond purity and color variations of solid gold, other gold-containing materials are encountered, differing significantly in composition and manufacturing. These are not “types” of solid gold but rather product categories that incorporate gold in different ways. Understanding these distinctions is important for assessing durability, value, and longevity.
Gold-plated items feature a very thin layer of gold deposited onto a base metal, commonly brass or silver, through electroplating. The gold layer, often 0.5 to 2.5 microns thick, is superficial and can wear off, revealing the underlying metal. This makes gold-plated jewelry more affordable, but less durable and long-lasting than solid gold or gold-filled pieces.
Gold-filled material involves a much thicker layer of gold mechanically bonded to a base metal core, usually brass, using heat and pressure. By US regulations, the gold layer must constitute at least 5% (1/20th) of the item’s total weight. This thicker layer makes gold-filled items more durable and resistant to tarnishing than gold-plated ones, offering a good balance of quality and affordability.
Vermeil, also known as “gold vermeil,” is a specific type of gold-plated material using sterling silver as the base metal. For an item to be classified as vermeil, it must have a gold layer at least 2.5 microns thick. While similar to gold plating in process, the sterling silver base provides a higher quality foundation, making vermeil a more premium option than typical gold-plated jewelry, though still subject to wear.