In the mid-1960s the introduction of wave forms into Riley’s work, as seen in Cataract 3, created a new set of possibilities, especially when combined with a cautious use of color. The interactions of different tones, often complementaries such as vermilion and turquoise, added variation to her earlier use of black and white. Wave forms were succeeded by stripes in the later 1960s and early 1970s (Rise 1), the stripes themselves often composed of tightly interwoven diagonals, adding another layer of complexity to their effects. [https://artuk.org/discover/stories/bridget-riley-top-of-the-ops#]