What’s inside Apple’s version of gold

At today’s event, Apple CEO Tim Cook gushed about the Apple Watch Edition’s “jaw-dropping, beautiful 18-karat gold.” He didn’t say much more, but the company’s website and patents offer additional detail about the metal in these high-end watches, which will sell for between $10,000 and $17,000.

By definition, 18-karat gold is 75% gold. Pure gold is 24-karat, which is so soft and malleable that it’s relatively rare to be used in jewelry and watches. Watch and jewelry companies typically make 18-karat gold and other alloys with different combinations of metals such as gold, silver, copper, and zinc. Both Rolex and Tiffany have trademarked names—Everose and Rubedo, respectively—for their proprietary rose gold alloys.

A video on Apple’s website specifies that the Apple Watch Edition comes in yellow and rose gold custom alloys that contain silver, copper, and palladium, “designed to be not only beautiful, but up to twice as hard as standard gold.” The video doesn’t mention what other components might be present. But Apple has a patent that suggests those custom 18-karat golds may also contain some ceramic powder—made of brittle, non-metallic materials such as garnets, boron carbide, silicon carbide, aluminum nitride, or even diamonds.

Some have suggested this is a clever way for Apple to save money by making an alloy that contains less gold by volume. But Apple’s patent points out other possible benefits, including scratch-resistance, high polish, and color selection. (Rolex has also patented the use of some ceramic powders to achieve difficult colors for its watches.)

If Apple is indeed using the ceramic technology it patented in December, the company isn’t advertising it. (We’ve contacted Apple for comment and will update if we receive more information.) Apple’s video does say its gold is designed to be “up to twice as hard as standard gold.” The patent for its custom 18-karat gold indicates a hardness of at least 400 HV on the Vickers Scale. Which is to say, pretty hard—although at the soft end of the snail tooth spectrum.

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