Gold has been prized for centuries, yet its appearance in shades like white, rose, and green often causes confusion. Pure gold possesses only one color: a rich, warm yellow. The variety of colors seen in jewelry is not a natural property of the element, but a deliberate alteration achieved by blending the gold with other metals. This process allows manufacturers to create a spectrum of hues while maintaining the desirable qualities of the precious metal.
The Science of Pure Gold’s Yellow Hue
Pure gold (24-karat) exhibits a unique yellow color because of how its atoms interact with visible light. Most metals, such as silver and platinum, appear silvery-white because their electrons reflect all wavelengths of light equally.
The large atomic nucleus of gold causes its innermost electrons to move fast enough to experience relativistic effects, altering the structure of the outer electron orbitals. This change reduces the energy required for electrons to jump to a higher level. Consequently, gold atoms absorb light in the blue and violet part of the spectrum, causing the remaining reflected light to appear yellow to the human eye.
The Role of Alloying in Color Change
Because pure 24-karat gold is naturally soft and easily damaged, it is almost always mixed with other metals to increase its strength and durability for use in jewelry. This process creates an alloy, where secondary metals (alloying agents) fundamentally change the gold’s physical and optical properties.
The addition of metals like copper, silver, or palladium introduces new atoms into the gold’s crystal structure, which disrupts the original electron configuration. This disruption alters the metal’s ability to absorb and reflect certain wavelengths of light. By carefully controlling the type and percentage of the alloying agents, manufacturers can manipulate the gold’s optical response, resulting in a visible color shift away from the pure yellow.
Categorizing Gold Colors by Composition
The specific color of alloyed gold depends entirely on the metals it is mixed with and the proportions used in the blend. The most popular alternative colors are white, rose, and green gold, each achieved through a distinct metallic recipe.
Rose gold, also known as pink or red gold, gains its warm flush from a high concentration of copper. For instance, 18-karat rose gold contains 75% gold, with the copper content directly responsible for the pinkish hue. White gold is created by blending pure gold with “white” metals such as palladium, nickel, or zinc to neutralize the yellow color. While this alloy is naturally pale, it is typically plated with rhodium to achieve the bright, mirror-like finish commonly seen in jewelry.
Green gold is produced by mixing gold primarily with silver, sometimes with a small addition of copper or cadmium. The silver absorbs some of the red light, pushing the reflection toward a subtle, pale greenish-yellow tint.
Understanding Karat and Color Intensity
The purity of gold in an alloy is measured using the karat system, which is based on a scale of 24 parts. For example, 24-karat gold is 100% pure, 18-karat gold is 75% pure, and 14-karat gold is 58.3% pure. The karat level determines the ratio of pure gold to the alloying agents, which directly impacts the intensity of the final color.
A lower karat number means a higher proportion of alloying metals are present in the mixture, intensifying the non-yellow hue. For example, 14-karat rose gold contains a larger percentage of copper than 18-karat rose gold, resulting in a deeper pink or reddish color. Conversely, a higher karat content, such as 18-karat white gold, will have a more noticeable warm, pale-yellow undertone because the greater amount of pure gold dilutes the effect of the white alloying metals.