The Patient Eye: why a Sunday afternoon took two years to finish drying.

Notes from the studio on building a colour palette the retina has to finish for you — and why every dot is worth the wait.

I spent the winter of 1885 standing about two metres from a single unfinished canvas, holding a fine sable, placing one dot of cadmium-green beside one dot of rose-madder and stepping back to see if the lawn read warmer. It did, faintly. Then a dot of cobalt for the shadow under a parasol; then a dot of pale chrome for where the same parasol caught the afternoon. The painting did not progress in figures or scenes. It progressed in pairs.

Chevreul, in the margin

Above my workbench is a folded page from Chevreul's 1839 treatise on simultaneous contrast, the binding cracked at the chapter on complementaries. Renoir uses it as a footnote; we treat it as a recipe. A green is never simply green — it is a green dot at thirty percent saturation, set a hair away from a magenta dot at thirty percent, so the eye, at three paces, fires a third hue the brush itself never mixed. The lawn at the centre of the Grande Jatte canvas is, on the easel, lawn-green and walkway-cream; from the gallery bench it is a noon that hums.