The International Gem Society (IGS) published an article about the issue of underkarating and how, despite federal laws, many merchants are advertising and promoting sales of gold at a much higher karat level than the buyer is actually receiving. The U.S. Federal Trade Commission offers guidance on gold jewelry, what karat quality mark to look for, and what each number means. According to their website, pure gold is 24 karat (24K) gold. But gold is soft, so it’s often mixed with other metals to increase its hardness and durability. When that is the case, the total of pure gold and other metal adds up to 24, so:
- 18K gold is 18 parts gold mixed throughout with 6 parts other metal
- 14K gold is 14 parts gold mixed throughout with 10 parts other metal
- 10K gold means 10 parts pure gold and 14 parts other metal
Those other metals usually consist of copper, zinc, silver, tin, etc. When a metal is made by combining two or more metallic elements, it is called an alloy. Gold plating describes jewelry that has a layer (at least .175 microns) of at least 10 karat gold applied on a base metal. (We explained how to plate jewelry in this previous article How Gold Plating is Done, Step by Step.) Of course, the higher the karat, the more valuable it is.
But it’s not just the value of the piece that is a concern with underkarating. As we mentioned, metal alloys are created to impart many properties, such as strength, flexibility, machineability, and durability. But it is important that the correct ‘recipe’ of metals be used in order to ensure that the finished piece doesn’t easily corrode or break. A Santa Barbara jeweler, Calla Gold, admits she is not expert enough to know about alloy metals and their specific effect on rings, but she does know that there can be detrimental results when the wrong material is used.
“When rings go bad I can see porosity, I can’t see that a particular metal choice caused a problem. I’m often left in a mystery, wondering why that ring cracked. Was it a pooled alloy metal that was too brittle? I don’t know. But when a ring of proper thickness bends or cracks I do suspect that something about its alloying or casting was the culprit.”
Using the correct elements for alloying is critical to many manufacturing operations. Although not pieces of jewelry, metal fasteners, such as screws, nuts, bolts, and clamps, are critical components in many industries, and if made with the wrong alloy can result in costly or even catastrophic consequences. (Read XRF for Alloy Verification Improves Safety of Metal Fasteners.)
Calla is a fan of alloyed materials for strength and durability for jewelry, if it’s the correct alloy. She, however, has seen some aesthetic problems with incorrectly alloyed material. “I have actually found 10kt gold to be more sturdy in some examples of jewelry. However, pieces can get discolored and lose their visual appeal. I have seen the yellow gold color change to a more rose gold look, but the coloring is more like a brick, not a pretty pink. I’ve found jewelry that oxidized and produced an unpleasant browny red color after the jewelry had been worn for awhile.”
With the volatility and high price of gold and other precious metals, many business owners are turning to portable x-ray fluorescence (XRF) analyzers to perform precious metal testing on their jewelry pieces to confirm they are working with, buying, and selling the correct karated and alloyed materials.
XRF is a nondestructive testing technique that can analyze a metal sample in seconds with little to no need for sample preparation. Portable XRF analyzers deliver fast, accurate elemental analysis and karat amounts in seconds. In fact, advances in handheld XRF technology have expanded to the point that today’s analyzers are capable of distinguishing alloy grades that are nearly identical in composition to one another. And the testing is non-destructive to the piece – another benefit to jewelry industry.
- Read the articles:
- Watch the two featured portable precious metal testing videos.