Using a ruler and pencil, mark points at 30cm intervals along the wall. Draw vertical lines at these points. Next mark horizontal lines up the wall at 10cm intervals. Join the 10cm widths diagonally. Using painter's tape, tape off random sections and paint with one colour. When dry, peel off tape. Meanwhile, tape other sections and paint with a different colour. Repeat to use three paint colours, remembering to leave some of them white. Photography Chris Warnes