TierraCast's Hypoallergenic Earring Hooks are made from Niobium! TierraCast's Hypoallergenic Earring Hooks 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 Earring Hooks are also called Ear Wires.