By 1946, Tesoro had risen to head the organic synthesis department at Onyx Oil and Chemical Company.
By 1946, just two years after joining Onyx Oil and Chemical Company, Giuliana Tesoro had been promoted to head of the organic synthesis department. This rapid ascent underscored both her scientific talent and the value her employer placed on her innovative research into textile and fiber chemistry.
Leading a research department at a chemical company during the mid-1940s was an unusual accomplishment for a woman, especially one who had immigrated to the United States only a few years earlier. In this leadership position, Tesoro directed research efforts focused on the synthesis of new organic compounds for industrial textile applications, work that would form the technical basis for many of her later patented inventions in flame retardants, antistatic treatments, and specialty fibers.
Her promotion at this early career stage reflects the meritocratic recognition of her scientific abilities within the company, even as broader American industry remained largely closed to women in comparable leadership roles. Her tenure heading this department helped set the stage for her continued rise at Onyx, culminating in successive promotions to associate director and assistant director of research over the following decade.