The ring is made of Egyptian blue, which was a vibrant blue pigment, considered to be the first synthetically-produced pigment, composed of quartz sand, a copper compound, and calcium carbonate. The color blue was highly prized in ancient Egypt and the creation of a synthetic pigment allowed artists to produce imitations of the precious stones lapis lazuli and turquoise, which were expensive and not always readily accessible.
New Kingdom, 18th Dynasty, ca. 1550-1077 BC. Now in the Private Collection.