Alloying: Exotic Gold Colors and Gold Purity
Modified: April 2011
by Jerry Sisk, GG; Co-Founder, Jewelry Television®
Have you ever wondered how gold jewelry is manufactured in different colors? You are probably familiar with the traditional yellow, white, and rose gold, but did you realize that other gold colors exist?
Although much rarer and exotic, gold in colors such as blue, purple, red, and various shades of green are possible. This is done through the science of alloying.
Alloying: Creating Colored Gold
Let's explore some of the exotic colors of gold. To produce green gold, varying amounts of silver, copper, and cadmium may be alloyed in differing percentages to create a range of green gold shades. Gold in pinks to reds requires varying amounts of copper and silver. Some gold colors, such as purple and blue, contain aluminum and iron, respectively. These gold colors are much more difficult to produce but are stunning in appearance.
It is important to note that certain minimum percentages of metallic elements are needed to create some of the more exotic colors. Therefore, certain colors may be limited to 10kt, 14kt, or 18kt. Generally white, rose, and yellow gold are available in all three karatages. Whatever your preference, alloys can provide a wide range of colors and shades that are certain to satisfy even the most demanding individual.
Now, back to the subject of alloys.
Alloys: Gold Fineness and Purity
Gold's fineness is measured in parts per thousand. In practical terms, gold can be refined to approximately .999 purity. However, for jewelry purposes, other metals are added to gold to form a mixture or alloy that is more durable and useful for manufacturing. In terms of gold jewelry, the fineness of gold is designated in karats, which is commonly abbreviated with "kt" or "K."
Base metals are the more common metallic elements, like copper, zinc, and nickel, that are used to alter the appearance and/or durability of the alloy. A second group, called noble or precious metals, includes gold, silver, and the platinum group.
To determine the percentage of gold in any piece of jewelry, simply divide the karat content by 24 and multiply by 100. Therefore, 18kt is .750 pure (18/24 x 100) or 75 percent gold. So, 10kt and 14kt are 41.7 percent and 58.3 percent gold, respectively. The remainder may be any combination of base or noble metals.
While the amount of pure gold is standardized for all karat gold jewelry, there are no fixed guidelines for the types and percentages of base or precious metals alloyed. Many manufacturers make 18kt white gold products, although the process is somewhat like creating a cake. While a basic recipe exists, some ingredients may be substituted or replaced as needed.
In the case of 18kt white gold, a manufacturer might use a combination of nickel, copper, and zinc, or when creating nickel-free gold, a combination of palladium and silver would be used. Once again, the amount of pure gold (75 percent) does not change, just the types and percentages of the other alloys added to it. There are as many recipes for 18kt white gold as there are for apple pie.
Characteristics of Gold
While gold's characteristics are important to various industries, the fact that gold is malleable, ductile, and corrosion resistant is important to jewelry manufacturers.
Malleability: Gold is so malleable that it can be hammered out into extremely thin sheets. In fact, an ounce of gold can produce a sheet so thin that it can cover 100 square feet. Gold leaf, used to adorn buildings and embellish objects, is one application of gold's malleability.
Ductility: A second quality of importance to jewelers is gold's ductility, or its ability to be drawn into very thin wires without breaking. One ounce of gold can produce a wire nearly five miles long. Intricate pieces of handmade gold jewelry are possibly due to gold's ductility.
Corrosion Resistance: Jeweler's appreciate gold's third important quality: resistance to corrosive elements. No single acid and very few chemicals will react with gold, making it extremely stable and long lasting--and ideal for gold jewelry.