Until recently, gold, silver, bronze, and copper were made with metal filings. These inks were difficult to use in a broad edge pen and they were not archival. The newer method is to use mica for the sparkle.
Gold has mica particles to give the sheen and an earth color pigment to give the gold tone.
These mica based products have a high permanence of color. They also have a finer grind making them easier to write with. Holbein, and Schmincke metallics seem to be mica based products. Writing with gold is not as easy as writing with ink. Carol Pallesen Hicks likes the Yasutomo pan colors.