Frank Stella began his “Protractor” series in the late 1960s, painting bright, curved bands of color on large canvases cut to resemble the semi-circular shape of protractors. With bold, rainbow palettes, the “Protractor” series marked a creative turning point for the Minimalist artist—until then, Stella was known for his muted “Black Paintings” composed of monochromatic stripes and rectilinear shapes. Stella was inspired to experiment with circular curves after a 1963 trip to Iran left him fascinated by the rounded and brightly colored patterns of Islamic art. Hinting at his original influence, Stella titled his “Protractor” paintings after ancient cities in Asia Minor, such as Khurasan, Basra, Damascus, and Harran. Though Stella completed his ninety-third and final “Protractor” painting in 1970, he continued to create print series inspired by the shape of the drafting tool, such as his “Newfoundland Series” (1971), “Sinjerli Variations” (1977), and “Polar Coordinates” (1980).