NL Industries , formerly known as the National Lead Company, is a lead smelting company currently based in Houston, Texas. National Lead was one of the 12 original stocks included in the Dow Jones Industrial Average at the time of its creation on May 26, 1896. It began business in Philadelphia in 1772. The name "National Lead Company" was used since 1891 after a series of mergers. National Lead changed its name to NL Industries in 1971.