Edge, 1967, belongs to Cohen’s rhombus paintings, a group of the mid-1960s in which he turned the square canvas on its point. Two of them, Sentinel and Consul (both 1966), were shown at the Venice Biennale. By 1967 line, which in the paintings of 1962–64 had divided the surface into territories, had all but gone: over a red-brown ground, spattered and sprayed, an even canopy of blue dots runs from corner to corner.

Cohen presented this body of work in Harold Cohen: New Paintings at the Museum of Modern Art, Oxford, from 18 June to 13 July 1968, and wrote the introduction to its catalogue himself. In an interview for Studio International the same year, he explained that colour had become central to his work only gradually, and at first against his own instincts. Line served to separate and divide, while colour offered cohesion. The rhombus format returned several years later in Cohen’s earliest computer-generated drawings on paper.