Tesoro began her industrial chemistry career at Onyx Oil and Chemical Company, launching decades of textile chemistry innovation.
In 1944, shortly after completing her doctorate at Yale, Giuliana Tesoro accepted a position as a research chemist at Onyx Oil and Chemical Company. This role marked her entry into industrial chemistry, a sector where women scientists were exceedingly rare, particularly in technical and research leadership roles.
At Onyx, Tesoro began the work that would define much of her career: the chemistry of synthetic fibers and textile treatments. Her research focused on developing chemical processes to improve the performance characteristics of fabrics, including flame resistance, static control, and dye affinity — innovations that would later find widespread application in consumer and industrial textiles.
Her hiring at Onyx represented an important, if quiet, breakthrough for women in industrial chemical research, an arena overwhelmingly dominated by men in the 1940s. Tesoro's scientific rigor and creativity quickly distinguished her, and she would go on to rise through the company's ranks over the subsequent decade, eventually being placed in charge of key research divisions. This period at Onyx became the foundation of a research career that ultimately produced over 125 patents in polymer and textile chemistry.