Cobalt is a hard, scratch resistant, hypoallergenic material that is 4 times harder than platinum and 5 times harder than gold. It is shatterproof and will never chip, crack or discolor. Cobalt ring cannot be resized. Cobalt is offered in its natural white or with a black DLC coating. The black coating is baked onto the cobalt at very high temperatures creating a durable scratch resistant, hypoallergenic coating.