What does the mark "417 GS" mean on gold?

A piece of gold stamped "417 GS" is likely to be made from a low-concentration gold alloy. European goldsmiths avoid the American convention of stamping gold by karat, preferring a more precise decimal metric. In Europe, a gold piece labelled "417" is 41.7 percent pure gold, or 10-karat.

In the United States, 10-karat is the lowest concentration that can legally be sold as gold, as of 2014. The "GS" stamping is an abbreviation for "gold shell," which indicates that the piece is plated with a layer of gold rather than containing solid gold throughout. A 417 GS piece of jewelry, therefore, is probably made of a base metal and coated with 10-karat gold.