Greenberg had argued that the most modern paintings were abstract, two-dimensional, and without any sort of literary or narrative content. He believed that modern painting should embrace the two-dimensionality of the support and not attempt to subvert it illusionistically, like figurative art. He went further to say that any allusion to the outside world would hinder the raw emotional or psychological impact of the forms and colors.
For this reason, he was an early advocate of Pollock, whose drip paintings had challenged the idea of representation to a new degree through the non-descriptive pouring of paint onto a horizontal canvas.
By 1952, however, when Greenberg was looking for a next step beyond the gestural application of Abstract Expressionism, Frankenthaler showed him a new kind of picture she had made through a pouring method she had developed—which she dubbed the “soak-stain.” Frankenthaler would thin oil paints with turpentine (later, she would thin acrylics with water) and pour them directly onto a flat canvas in broad patches, allowing the liquid to soak into the fibers of the support.
The resulting image remained as two-dimensional as its support, its pigments in rather than on the canvas. Mountains and Sea (1952), perhaps her most famous work, exemplifies this approach. Frankenthaler finished it off with some abstract gestures from a charcoal pencil.