It was only when I walked upstairs at the Tate and saw the thickly coagulated pigment of works by Frank Auerbach that I realised how much I had appreciated the beautiful sensuality with which Barbara Hepworth used materials, not just the smooth forms of abstract marble in the mid-1930s, juxtaposed together, but, most especially, her use of wood – holly and lignum vitae, smooth and beautifully polished – and her abstract shapes hollowed out in inverse, sometimes held together in tension with string, from later in the same decade.