Blackline was only invented at the end of the XXth century and absolutely revolutionized what it was thought possible to do with materials. It is a technique still used to treat the surface of pacemakers and other medical equipment that comes into close contact with the body. Blackline jewelry is produced by adding a surface layer of black and highly durable titanium film to a titanium core. The jewelry is resistant to wear and causes little friction to body tissue, making an allergic reaction highly unlikely to happen.