In the mid-1980s, Judd began to use a greater range of colours in individual works. Having discovered a factory inSwitzerlandthat could enamel thin sheets of aluminium in various colours, he began to create a series of horizontal wall-based sculptures which explore both colour and volume. Each one consisted of individually-coloured units of three given standard lengths, 30, 60 and 90 cm, attached together to form an elongated box, two rows in height. 

The colours were selected from an industrial colour chart, and enamel-baked on to the aluminium sheets before the work was assembled. In the earlier works of this series, reds and yellows predominate, but in strikingly different tones. As Judd developed the idea, so the works became more complex, both in the arrangement of different-sized units, and in increasingly intricate patterns of adjoining colours. One work shown here consists of two panels, one placed above the other so that the colours spread and respond to each other across four vertical levels rather than two. 

The way that each colour related to the others was of paramount importance to Judd. He was determined to avoid the most obvious harmonies or contrasts. ‘I didn’t want them to combine’ he later wrote, ‘I wanted a multiplicity all at once’. These principles are equally evident in the larger floor-based works in which each colour forms a striking pattern across the entire surface of the sculpture to almost overwhelming sensory effect, as the carefully-mapped, interlinking areas of colour simultaneously greet the eye.