TierraCast's Hypoallergenic Ear Wires are made from Niobium! TierraCast's Hypoallergenic Ear Wires come in a variety of colors including brass, copper, black, and more. NIobium is known to be a hypoallergenic material that is less irritating for sensitive ears than sterling silver, gold, or copper. TierraCast's Ear Wires are also called Earring Hooks.