Gold, a metal cherished across cultures and centuries, is universally recognized for its distinct warm, yellow hue. The idea of gold appearing silver might seem contradictory. Yet, in jewelry and metallurgy, gold can be transformed to exhibit a bright, silvery appearance. This transformation involves scientific principles, allowing gold to take on a different visual identity.
Why Gold is Gold
The characteristic yellow color of pure gold stems from the unique behavior of its electrons. Unlike most other metals, gold’s electrons absorb light in the blue and violet parts of the spectrum. This absorption is due to relativistic effects, where electrons moving at extremely high speeds around the heavy gold nucleus experience a change in their energy levels. When blue light is absorbed, the remaining light reflected back to our eyes is predominantly yellow and red wavelengths. Silver, for instance, has lighter atoms and its electrons do not experience these same relativistic effects, causing it to reflect light more uniformly across the visible spectrum, resulting in its silvery-white appearance.
The Alloying Approach: White Gold
To achieve a silver-like appearance, gold is combined with other metals in a process called alloying. White gold is not a naturally occurring metal but an alloy, a mixture of pure gold and at least one white metal. Common white metals used include palladium, nickel, silver, and sometimes manganese or copper. These added metals dilute gold’s natural yellow color and contribute to a lighter, silvery hue, while also enhancing the metal’s strength and durability.
The proportion of pure gold in white gold is measured in karats. For example, 18K white gold contains 75% pure gold, while 14K white gold contains 58.5% pure gold, with the remainder being the white metal alloys. The specific blend of alloying metals influences the final color, which can range from a pale yellow to a grayish-white, rather than a pure bright white. Some individuals may also experience skin reactions to nickel-containing white gold alloys, leading to the development of nickel-free formulations.
The Surface Approach: Plating
Despite the alloying process, most white gold alloys do not achieve a perfectly pure white color on their own. To enhance their whiteness and provide a brighter finish, white gold jewelry is commonly coated with a thin layer of rhodium. Rhodium is a naturally bright, silvery-white metal belonging to the platinum family, known for its exceptional brilliance and durability.
This coating is applied through an electroplating process, where the jewelry piece is submerged in a rhodium solution and an electric current causes the rhodium ions to bond to the surface. The rhodium layer is extremely thin. While rhodium plating significantly improves the aesthetic appeal and scratch resistance, it is not a permanent solution and will gradually wear off over time, revealing the underlying, slightly yellowish white gold alloy.
Maintenance and Identification
Maintaining the silvery appearance of white gold requires specific care. Regular cleaning with mild soap and warm water using a soft brush helps remove dirt and oils. It is advisable to avoid exposure to harsh chemicals found in household cleaners, swimming pools, and some beauty products, as these can accelerate the wear of the rhodium plating or discolor the underlying alloy.
Since rhodium plating wears off, periodic replating is often necessary to restore the jewelry’s bright white finish. When identifying white gold, look for hallmarks or stamps. These markings indicate the karat weight, such as “10K,” “14K,” or “18K.” Unlike silver, white gold does not tarnish, and a simple magnet test can help differentiate it from other metals, as true white gold is non-magnetic.