If someone buys a piece of jewelry that is 18K HGE, they are essentially buying a piece of jewelry that has been plated with 18K gold. HGE stands for heavy gold electroplate, and 18K or 18 karat refers to gold that contains 75 percent gold and 25 percent other metals.
HGE 18K jewelry has so little gold on it that it is often considered to be costume jewelry. The number "18" in the phrase "18K" refers to the fact that 18K gold is made up of 18-parts gold and six-parts other metals. Solid gold is referred to as 24K gold as it is 24-parts gold.