metzinger's response in "coucher de soleil no. 1", in addition to illustrating actual radiation emanating in concentric circles from the sun, was to separate colors in such a way as to avoid mixtures, leading to inert tones. contrary to the impressionists related hues, often placed on top of one another while still wet—leading to a result the divisionists found dull—contrasting hues placed side by side for the effect or creating optical vibrations were essential to divisionists.