To make red gold we remove silver and add only copper. View of two 14k yellow gold chains whose yellow hue varies due to the composition of the alloy. Yellow gold ring with purple gold inlay (original photo). Like the other colors of gold, black gold is created by adding a darker colored metal to the mix.
Sometimes iron or titanium can be used. However, most often it is achieved with cobalt that forms an oxide layer on the surface of gold when heated between 700 and 950 degrees Celsius. Since copper has a deep pinkish orange color, the addition of this alloy to gold gives gold a beautiful rose gold color.