Bridget Riley is one of Britains best-known artists, celebrated since the mid-1960s for her distinctive, optically vibrant paintings, called “Op Art.” She exploits optical phenomena so that a work appears to flicker, pulsate or move. The vibrant black-and-white optical pattern paintings, which she painted in the 1960s, were hugely popular and became almost a hallmark of the period. She is interested in visual effects, commenting: the eye can travel over the surface in a way parallel to the way it moves over nature. It should feel caressed and soothed, experience frictions and ruptures, glide and drift One moment, there will be nothing to look at and the next second the canvas seems to refill, to be crowded with visual events. White Disks,” 1964, Bridget Riley. She wrote that “…the uncertainties of a drawn structure increase when it is composed of similar, repeated elements. Because they are small and compacted, these elements begin to fuse while they are easy to separate when they are big.” Movement of Squares Bridget Riley is one of the finest exponents of Op Art, with her subtle variations in size, shape and position of blocks within the overall pattern. Her work is characterised by its intensity and its often disorientating effect. Indeed the term 'Riley sensation' was coined to describe this effect of looking at the paintings, especially her early black and white pictures. Riley is fascinated with the act of looking and in her work aims to engage the viewer not only with the object of their gaze but also with the actual process of observation. Bridget Riley Horizontal Vibration, 1961 Tempera on Hardboard, 171/2x551/2 in Simultaneous contrast is most intense when the two colors are complementary colors. Complementary colors are pairs of colors, diametrically opposite on a color circle red and green, blue and yellow as seen in Newtons color circle. Yellow complements blue: yellow and blue lights, mixed, generate white light. For thousands of years, artists have exploited the effect of juxtaposing complementary colors, without understanding it in neurophysiological terms. Few artists have made as dramatic a use of complementary colors as Vincent van Gogh (1853-1890), illustrated below. Both were painted in Arles in the same month of 1888. Blaze 1 Fall Descending Arrest 1 Breathe Cataract 3 Orient 4