Bridget Riley has achieved international success with her abstract ‘Op art’ paintings. Initially making these works solely in black and white, she later began exploring colour. After a trip to Egypt in 1981, she began working in her 'Egyptian palette’, inspired by the country’s landscape and its ancient art. In this work, an early experiment in the effects of colour combinations, Riley carefully plotted the four colours on graph paper, including hand-written viewing instructions for the best optical effects.