White gold is an alloy, meaning it is not found in nature as a pure element. It is created by combining pure gold with other metals to achieve a specific color and improve its physical properties. Pure, 24-karat gold is naturally a deep yellow color and is too soft and malleable for practical use in jewelry. Alloying the gold changes the color from yellow toward white and significantly increases its hardness and durability. This process transforms the soft, yellow metal into a strong material with the popular silvery-white appearance suitable for everyday wear.
What Defines an Alloy?
An alloy is a homogeneous mixture of two or more elements, with at least one of them being a metal. The primary purpose of alloying is to produce a material with characteristics superior to those of the individual components. Atoms of different sizes are introduced into the primary metal’s crystal structure, which makes it harder for the atoms to slide past one another. This atomic interference results in a material with greater strength and resistance to deformation than a pure metal.
Pure gold, like other pure metals, is made up of atoms of a single size arranged in a highly regular structure, making it relatively soft. Introducing other elements disrupts this perfect arrangement, fundamentally changing the material’s engineering properties. The creation of an alloy allows manufacturers to precisely tune features like melting point, strength, and color for a specific application. Bronze (copper and tin) and steel (iron and carbon) are common examples of how mixing elements creates a vastly improved material.
The Metals Used in White Gold
White gold is created by mixing pure yellow gold with various white metals to bleach its natural hue and add strength. The purity of the gold content is measured by the karat system, where 24 karat is 100% pure gold. An 18-karat white gold alloy is 75% pure gold and 25% other metals, while a 14-karat alloy contains 58.3% gold and 41.7% other metals.
The remaining percentage consists of white metals like nickel, palladium, silver, or zinc. Nickel-based white gold is known for being very hard and strong, making it suitable for items like rings and pins, but it can cause allergic reactions in some individuals. Palladium-based white gold offers a higher quality, more hypoallergenic alternative, often exhibiting a slightly grayer tone than nickel alloys. Palladium alloys are also softer and more pliable, which makes them particularly good for setting gemstones. The choice of alloy metals dictates the final working properties and the underlying color of the white gold.
Why Rhodium Plating Is Essential
Even after alloying with white metals, the resulting white gold often retains a faint yellowish or grayish tint due to the presence of the original yellow gold. To achieve the brilliant, true white color, the jewelry is given a surface treatment called rhodium plating. Rhodium is a rare, naturally occurring metal that belongs to the platinum family and is known for its extreme whiteness and high reflectivity.
This thin layer of rhodium is applied through an electroplating process, providing a mirror-like finish that is highly resistant to corrosion and tarnishing. The rhodium plating also acts as a protective barrier, increasing the durability and scratch resistance of the jewelry. Because this plating is only a surface layer, it gradually wears away over time, especially on high-contact areas. Consumers must periodically have the piece re-plated, typically every one to two years, to maintain the bright, silvery-white appearance.