YOUNGSTOWN, Ohio – Today in Flashback, Brooke Testa, curatorial assistant for the Mahoning Valley Historical Society, highlights the evolution of flat irons. Used from the 17th century, early models were heated by fire or stove. Fuel irons, powered by gasoline or kerosene, appeared in the 19th century. Electric irons followed, with key developments in the 1880s and 1890s, becoming common by the 1920s.