Gold alloying mixes pure gold with other metals to create a material with different physical properties and colors. Pure gold is 24-karat (24K), representing 99.9% purity. When other metals are introduced, the gold content is proportionally reduced, measured by the Karat system. For instance, 18-karat gold contains 75% pure gold, while 14-karat gold is 58.3% gold. This system standardizes the purity of gold used in jewelry and other products.
The Necessity of Alloying Gold
Pure 24-karat gold is naturally soft and extremely malleable, making it unsuitable for durable objects like most jewelry. On the Mohs scale, pure gold scores only 2.5 to 3, meaning it can easily scratch, bend, or deform with daily wear. This softness is a significant problem, especially in settings meant to hold precious stones, as the metal could lose its grip. Alloying solves this inherent weakness by significantly increasing the material’s strength and resistance to wear. The resulting gold alloy can withstand the rigors of everyday use and allows manufacturers to adjust the melting point and control the final color.
Primary Metals Used in Gold Alloys
The choice of alloying metal directly influences the final properties of the gold, contributing specific traits like hardness, strength, and color modification. The most common metals used are copper, silver, nickel, palladium, and zinc.
Copper
Copper is widely used because it significantly increases the hardness and strength of gold. Its reddish-brown hue creates the spectrum of rose and red gold alloys. Adding copper also makes the alloy more susceptible to heat treatment, allowing for further hardening.
Silver
Silver is a fundamental component, particularly in yellow gold alloys, where it maintains malleability while lightening the deep yellow color of pure gold. As a noble metal, its inclusion helps maintain a high resistance to tarnishing. Silver and copper are often used together to achieve the desired balance of color and mechanical strength.
Nickel and Palladium
For white gold, nickel and palladium are the primary components. Nickel-based white gold is hard and strong, making it ideal for items like rings, but it can cause allergic reactions. Palladium is a more expensive alternative that tends to be softer and more pliable, often preferred for setting gemstones.
Zinc
Zinc is frequently included in smaller quantities, acting as a deoxidizer during casting to prevent imperfections. It also contributes to the hardening of the alloy.
Understanding Gold Coloration
The final color of gold is determined by the precise ratio and type of non-gold metals incorporated into the alloy. The natural yellow color is maintained in traditional yellow gold alloys by using a balanced mixture of silver and copper. Silver lightens the tone slightly, while copper adds warmth, resulting in the classic color seen in 14K or 18K yellow gold.
Rose or pink gold is created by significantly increasing the concentration of copper in the mixture. An 18K rose gold alloy sometimes contains up to 22.25% copper. The higher the copper content, the more intense the reddish hue becomes, ranging from a soft pink to a deeper red.
White gold relies on alloying with metals like palladium or nickel to inhibit the gold’s natural yellow color. Because gold is inherently yellow, white gold alloys often retain a slight yellowish tint, even with the addition of white metals. To achieve the bright, pure white finish commonly expected, the final piece is usually coated with a thin, hard layer of rhodium, a brilliant white metal. This plating enhances the visual whiteness and also provides an extra layer of durability to the surface.