Gold is considered a divinely valuable material in nearly every culture on earth, and luckily for artists, it's extremely malleable. Gold leafing is the practice of hammering out extremely thin sheets of gold, down to .1 or .2 microns, and using it to coat objects, or apply to an image, and artists and craftsman have been doing it for millennia.
Ancient Egyptians lined their pharaoh's tombs with gold leaf. Greek sculptures clothed the chrysoelephantine statues in gold garments and armed them with gold-leafed swords. In the Middle Ages, monastic scribes emblazoned hand-copied bibles with gold-leaf illustrations, and even more recent artists like Gustav Klimt have added gold to their paintings for that glossy hint of the divine.