When colours are twisted along the rise and fall of a curve their juxtapositions change continually. There are innumerable sequences each of which throws up a different sensation. From these I build up clusters which then flow into each other almost imperceptibly

An important innovation of Zing 1 1971 was the use of twisted stripes to create horizontal zones of coloured light. This is the result of changes in the width and position of different colour stripes. In order to develop this perception Riley needed to find a formal device that would increase the uneven interaction of colour. The vehicle for this progress was her adoption, in 1974, of the curve form as the basis of her paintings.

A broadening and deepening of Riley’s understanding of the relation of colour and light can be seen in her curve paintings. The key to this is the role of the curve in creating a more pliable, less assertive structure – one which readily recedes behind the play and movement of light – so that occasionally the effect is as delicate as stained glass. In Clepsydra 1976 and To a Summer’s Day 1980, the eye follows the course of a curve and loses the thread as the shapes fuse, dissolving like a rising haze of heat or undulating like ripples on water.

Such effects are non-descriptive but tantalisingly evocative, recalling the sensations and rhythms of nature. The curve paintings include some of the most serene and emotionally radiant works that Riley has ever painted, implications that blossom in the connotations of poetry and music contained in some of their titles. Surprising though it may seem, until 1978 Riley confined her palette to three colours within each painting. In the Song of Orpheus series 1978, Riley now expanded this to five colours which, animated by the curve form, draw the eye into a shimmering chromatic field.