The purity of the spectral element being the keystone of my.... searching for an optical formula on this basis ever, since I held a brush 1876-1884.... having read Charles Blanc in school and therefore knowing Chevreul's laws and Eugene Delacroix's precepts, having read the studies by the same Charles Blanc on the same painter [Delacroix] (in 'Gazette des Beaux-Arts', vol. xvi, if I remember correctly)

'Letter to Félix Fénéon', June 1890