On Oct. 26, 1952, a 23-year-old artist named Helen Frankenthaler made a painting on unstretched, unprimed canvas laid on the floor, using a freehand stain technique that owed a great deal to Jackson Pollock but was less systematic. She called it “Mountains and Sea,” and it became her best-known, most influential work. Its bounding scale, skirmish of pastel colors and charcoal lines, and mixture of landscape, still life and abstraction were distinctive. But most important was the way it fused color and canvas into a new, streamlined unity. Frankenthaler’s stain painting method, as it was sometimes called, was considered a breakthrough in many circles, the gateway to what would become Color Field abstraction.