 With his "Pietre (stones)" series, begun in 1952, Fontana fused the sculptural with painting by encrusting the surfaces of his canvases with heavy impasto and colored glass.In his "Buchi (holes)" cycle, begun in 1949–50, he punctured the surface of his canvases, breaking the membrane of two-dimensionality in order to highlight the space behind the picture.From 1958 he purified his paintings by creating matte, monochrome surfaces, thus focusing the viewer's attention on the slices that rend the skin of the canvas.