Orange, yellow, ochre, russet. At first, the colours are distinctly separate. But if you stare at one of the four squares for a little while and then broaden your gaze again to take in the whole, the different shades seem either more intense, or weaker. The impression that meets the eye vacillates between flat surface and spatial depth. Albers investigated the adjacency of colours and their various effects in countless variations. The former Bauhaus pupil and later teacher at Black Mountain College in North Carolina, the cradle of the American post-war avant-garde, worked exclusively with pure, unmixed, industrial paints. The square remained his basic pictorial element throughout his career.