Rio Grande was founded more than 60 years ago by my father, Saul Bell. A jeweler for more than 80 years, Saul was involved in every imaginable aspect of the jewelry industry, including manufacturing, diamond-setting, watch-making, wholesaling and retailing. He loved to share his vast knowledge of the jewelry-making process. My brothers, sisters and I still benefit daily from his knowledge and wisdom, and I hope to pass on some of what I have learned from him and from other master jewelers through this series of blog posts.
If you’re interested in casting gold items, two terms you’ll want to be familiar with are “gold alloy” and “master alloy.” Gold alloy (sometimes called pre-mixed gold alloy, gold casting grain, or karat gold) contains gold, while master alloys are composed of metals such as copper, silver, nickel, palladium and zinc that are intended to be alloyed with pure gold to make a gold alloy having desired physical properties such as karat, color, strength and density.
A karat gold alloy has a specific amount of gold such as 41.66% gold for 10K, 58.5% gold for 14K and 75% gold for 18K. These are the karat values recognized by the U.S. Federal Trade Commission, and these alloys can be stamped with a karat mark in the United States. Other countries have their own traditions and laws concerning gold alloys for jewelry. As a caster you have two choices: you can buy gold casting grain already alloyed to the desired color and karat or you can buy fine gold and master alloy and alloy them together in the correct proportions.
The advantage of buying karat gold casting grain is that it is already processed and tested to be sure the gold content is legal and the manufacturing processes are well controlled. The advantage of using master alloy to alloy your own karat gold is high flexibility and low inventory investment. You can have several master alloys on hand for different karat values and colors and pure gold grain. With these you can alloy what you need when you need it.
Beside the major alloying elements used to make a standard karat gold casting grain, i.e. copper, silver, etc., premium alloys can be made by adding minor additions to improve the physical properties and/or the casting characteristics of the metal. These premium alloys fall in two major categories, deoxidizers and grain refiners. Premium alloys can be obtained in either karat gold or as master alloy.
As a note of caution, we recommend that you never mix one gold alloy with another unless you are absolutely sure they are compatible. In times past most gold alloys were simple and one could get away with mixing unknown gold alloys, but today the gold alloys perform much better and are easier to use, but they are often not compatible to be mixed. This is especially true of palladium and nickel white gold alloys.
Got questions? I’d love to hear ’em and I’m always happy to talk about casting processes. If you cast gold pieces, do you use pre-mixed alloy or a master alloy? Have you tried mixing your own alloys, and if so, what was your experience with it? We’d sure be interested in hearing about it!