To the layman who asked, “What is impressionism?” Mauclair has given the most succinct answer in his book L’Impressionisme:  “In nature,” he declares, “no colour exists by itself.  The colouring of the object is pure illusion; the only creative source of colour is the sunlight, which envelops all things and reveals them, according to the hours, with infinite modifications...  The idea of distance, of perspective, of volume is given us by darker or lighter colours; this is the sense of values; a value is the degree of light or dark intensity which permits our eyes to comprehend that one object is further or nearer than another.  And as painting is not and cannot be the imitation of nature, but merely her artificial interpretation, since it has only at its disposal two out of three dimensions, the values are the only means that remain for expressing depth on a flat surface.  Colour is therefore the procreatrix of design...  Colours vary with the intensity of light...  Local colour is an error; a leaf is not green, a tree trunk is not brown...  According to the time of day, i. e., according to the greater or smaller inclination of the rays (scientifically called the angle of incidence), the green of the leaf and the brown of the tree are modified...  The composition of the atmosphere... is the real subject of the picture...  Shadow is not absence of light, but light of a different quality and of a different value.  Shadow is not part of the landscape where light ceases, but where it is subordinated to a light which appears to us more intense.  In the shadow the rays of the spectrum vibrate with a different speed.  Painting should therefore try to discover here, as in the light parts, the play of the atoms of solar light, instead of representing shadows with ready-made tones composed of bitumen and black...  In a picture representing an interior the source of light [windows] may not be indicated; the light circulating, circling around the picture, will then be composed of the reflections of rays whose source is invisible, and all the objects, acting as mirrors for these reflections, will consequently influence each other.  Their colours will affect each other even if the surfaces be dull.  A red vase placed upon a blue carpet will lead to a very subtle but mathematically exact exchange between this blue and this red; and this exchange of luminous waves will create between the two colours a tone of reflections composed of both.  These composite reflections will form a scale of tones complementary of the two principal colours.

“The painter will have to paint with only the seven colours of the solar spectrum and discard all the others;... he will, furthermore, instead of composing mixtures on his palette, place upon his canvas touches of none but the seven colours juxtaposed [Claude Monet has added black and white] and leave the individual rays of each of these colours to blend at a certain distance, so as to act like sunlight upon the eye of the beholder.”  This is called dissociation of tones; and here is a new convention; why banish all save the spectrum?  We paint nature, not the solar spectrum.