Ad Reinhardt was the great polemicist of Minimal Art, calling with visionary passion for an art that would express nothing but the idea, or essence, of art. In an article published in 1962 he wrote 'The one object of fifty years of abstract art is to present art-as-art and as nothing else, to make it into the one thing it is only, separating it and defining it more and more, making it purer and emptier. more absolute and more exclusive - non-objective, non-representational, non-figurative, non-imagist, non-expressionist, non-subjective.' About two years before this statement appeared, Reinhardt had found the concept of painting which for him fulfilled this ideal: a canvas exactly five feet square, divided into a grid of nine squares painted in very closely related shades of matt black. Some of the early paintings in this format were titled by Reinhardt 'Ultimate Painting'. and he continued to paint in this way until his death, his aim being, he wrote, '... to paint and repaint the same one thing over and over again, to repeat and refine the uniform again and again. Intensity, consciousness, perfection in art come only after long routine, preparation and attention.' Reinhardt's late paintings are not in fact absolutely identical, he seems to have started each one completely afresh and when seen together they exhibit considerable tonal differences. The initial appearance of these paintings is of a uniform matt black but after a time the spectator begins to distinguish the different tonal areas of the grid. What emerges is a cruciform shape created by Reinhardt's painting of the central horizontal line of squares in one tone, the four corner squares in a different tone. and the centre top and centre bottom squares in a third tone. The different tones are arrived at by mixing the black with a small amount of colour, in this case red for the corners, green for the central horizontal band, and blue for the other two squares. As has often been pointed out, Reinhardt's 'black' paintings, in spite of their rationality of structure, have a compelling mystery of presence stemming not least from the symmetrical cruciform structure hovering within them. In the end even Reinhardt admitted that his art was a visionary one: in 1961 he wrote 'Everything is square, cruciform, unified, absolutely clear ... All is one vast symbolism ... All images share the "state of identical form." '
Simon Wilson, Tate Gallery: An Illustrated Companion, Tate Gallery, London, revised edition 1991, p.257