The term “post-painterly abstraction” was coined by influential American art critic Clement Greenberg (1909–1994) to describe abstract art inspired by—but separate from—American abstract expressionism. His term encapsulated multiple categories 242 of abstraction, including (but not limited to) hard-edge painting and stain painting. Hard-edge painting, as exemplified by the work of artists Frank Stella (1936-) and Ellsworth Kelly (1923-), is characterized by large geometric areas of color with absolutely no blending. Colors transition abruptly from one to the next, such as in Stella’s Gran Cairo (1962), a painting composed of a colorful series of ever-smaller square outlines. The artist Helen Frankenthaler is known for championing the technique of staining the canvas with pure color, also considered to be a form of post-painterly abstraction. Post-painterly abstraction emphasizes the formal qualities of painting, such as shape and color. Artists experimented with shaped canvas, transforming the painting into an object, or sculpture. Post-painterly abstraction lasted until the 1970s when postmodern artists began to challenge the supremacy of modernist critic Clement Greenberg.