Gold overlay is a thick coating of gold that jewelers lay over metal jewelry. The process has been around for thousands of years, and jewelry that undergoes this process is more valuable than other types of jewelry that has gold added to it in a different way. In gold-plated jewelry, the gold is plated on top of the metal and doesn't last as long as gold overlay.
Nickel is not used in the gold overlay process, so the jewelry does not cause a nickel-allergic reaction. Gold overlay jewelry doesn't cause skin irritation or discoloration, unlike some gold-plated jewelry.
Jewelers use heat and pressure to forge the gold overlay onto the jewelry pieces. Brass is usually the medium used with gold to create the new alloy. Gold overlay is often less than 1/20th of the weight of the metal on the entire piece. The process used in gold overlay is the same process used for gold-filled jewelry.
Some countries, such as Canada, require that jewelry enhanced with gold overlay be stamped as such. The piece must include the weight of gold used in the overlay process using certain symbols, alerting customers to the fact that the piece is not solid gold.