Colored Gold

While pure gold is yellow in color, colored gold can be developed into various colors. These colors are generally obtained by alloying gold with other elements in various proportions.

For example, alloys which are mixed 14 parts gold to 10 parts alloy create 14-karat gold, 18 parts gold to 6 parts alloy creates 18 karat, and so on. This is often expressed as the result of the ratio, i.e.: 14/24 equals 0.585 and 18/24 is 0.750. There are hundreds of possible alloys and mixtures, but in general the addition of silver will color gold white, and the addition of copper will color it red. A mix of around 50/50 copper and silver gives the range of yellow gold alloys the public is accustomed to seeing in the marketplace. A small amount (0.2%) of zinc can be added to harden the alloy.

The most common grades of gold, in addition to pure 24K, are 22K (92%), 18K (75%), 14K (58%), 10k (41%) and 9K (38%).

Colored golds can be classified to three groups:

• the Au-Ag-Cu system, producing white, yellow, green and red golds; typically malleable alloys
• the intermetallic compounds, producing blue and purple golds, as well as other colors. These are typically brittle but can be used as gems and inlays
• the surface oxide layers, such as black gold; mechanical properties depend on the bulk alloy, and the colored surface is prone to wear