Gold is a chemical element, represented on the periodic table by the symbol Au. When consumers ask about the “types” of gold, they are usually referring to classifications based on composition, appearance, or intended use. Pure gold is a soft, dense, yellow metal prized for its resistance to corrosion and tarnish. Because its physical properties make it unsuitable for daily wear, it is often alloyed with other metals. These alloys create classifications with varying levels of purity, distinct colors, and specific structural applications, which are categorized by purity, color, and structure.
Defining Gold Purity (The Karat System)
Gold purity is measured using the traditional karat system (K). This system divides the total mixture into 24 parts. Pure gold, designated as 24K, consists of 24 parts gold and is at least 99.9% pure by mass. However, this high purity results in a metal that is highly malleable and soft, making it susceptible to scratching and deformation in jewelry intended for everyday use.
For increased durability and strength, gold is mixed with other metals, which reduces the karat number. A common standard for fine jewelry is 18K gold, containing 18 parts pure gold and 6 parts alloying metals (75.0% gold content). A more durable and affordable option is 14K gold, which contains 14 parts gold and 10 parts alloy (58.3% pure). The lowest purity commonly sold as gold jewelry is 10K, which is 41.7% pure gold.
While the karat system is prevalent in North America, many international markets use the millesimal fineness system to denote purity. This system expresses gold content in parts per thousand and is often stamped on jewelry as a hallmark. For instance, 24K gold is marked as 999, 18K gold is 750, and 14K gold is marked with 583 or 585.
Gold Colors and Alloying Metals
Gold’s color variations are determined exclusively by the type and proportion of metals alloyed with the pure gold content. The purity or karat rating remains the same regardless of the final color; for example, 14K white gold has the same gold content as 14K yellow gold. These color changes are created by manipulating the non-gold portion of the alloy through metallurgical processes.
Yellow Gold
Yellow gold maintains its traditional hue by being alloyed primarily with copper and silver. These metals slightly harden the gold while preserving its characteristic appearance. Adjusting the relative amounts of copper and silver can produce different shades, but the final product retains the classic color. This variety closely resembles pure gold and requires no maintenance to retain its color.
White Gold
White gold is produced by mixing pure gold with white metals such as palladium, nickel, or manganese, which bleach the gold’s natural yellow color. Nickel alloys are generally harder, while palladium alloys tend to be more hypoallergenic. The resulting metal often has a pale, yellow-gray tint. Therefore, almost all white gold jewelry is coated with rhodium plating, which provides the bright, reflective white finish consumers expect but must be reapplied every few years as it wears away.
Rose Gold
Rose, or pink, gold achieves its distinctive reddish hue through a higher concentration of copper in the alloy mixture. Increasing the proportion of copper allows the alloy to absorb the reddish tint, creating a warm, rosy color. The intensity of the pink shade is directly proportional to the amount of copper used. This color requires no additional plating and its appearance is permanent.
Layered and Plated Gold Classifications
Beyond solid gold alloys, a separate category exists for items where gold is a surface layer over a base metal. These structural classifications are important for understanding the item’s value, durability, and longevity. They are differentiated by the thickness of the gold layer, the application method, and the composition of the underlying material.
Gold Plated
Gold plated items have the thinnest layer of gold, applied through electroplating. This process bonds a microscopic layer, typically less than 0.5 microns thick, onto a base metal like copper or brass. Due to this minimal thickness, gold plated items are the least durable, and the gold layer wears away quickly, exposing the base metal underneath.
Gold Vermeil
Gold vermeil is a more durable, legally regulated classification requiring two conditions. First, the base metal must be sterling silver (92.5% pure silver). Second, the gold layer must be a minimum thickness of 2.5 microns and be at least 10K gold. The sterling silver base makes vermeil a higher quality product than standard plating, offering greater longevity.
Gold-Filled
Gold-filled items provide the greatest durability among layered classifications. This involves mechanically bonding a thick sheet of gold to a base metal, such as brass, using high heat and pressure. To be legally classified as gold-filled, the gold layer must constitute at least 5% of the item’s total weight. This substantial layer makes gold-filled jewelry highly resistant to tarnishing and wear, positioning it as the closest alternative to solid gold.