Containing only trace amounts of chlorides and other halogens, these markers safely write on materials that are prone to stress cracking, such as stainless steel and titanium. Also known as T.E.C. markers, their ink is trace element certified. They meet standards for quality at aerospace manufacturers such as GE and Rolls-Royce, and are also used in the electronics and nuclear energy industries. Each marker is stenciled with the ink’s batch number for traceability. They work best on clean surfaces.