It's worthless According to Jewellery.com's inquiry, the main material for electroplating copper 18k gold is still brass. Although there is a thin layer of 18k gold on the outside in vacuum, this kind of jewelry can't keep its color for a long time. Wearing it for a long time will fade and reveal the color of brass inside. Moreover, brass itself is a relatively cheap metal without any corrosion protection. Therefore, copper plating 18k gold is worthless.