Oxidized silver is a process that many jewelers use to give sterling silver a black patina. It gives the jewelry an antique or tarnished look. The process consists of taking clean sterling silver and using a chemical (liver of sulphur) to treat it to speed up the tarnishing effect.
Although this process isn't permanent, it will wear beautifully. The wear over time will become unique to you since it reflects how you've used it in your life.