This, though a wholly practical reason for the growing popularity of tonal art is one of the powerful considerations for the trend from that sort which is liable to create discord. The simplest illustration of harmony, and unity and tone may be had in nature herself, for though these qualities have their scientific exposition, the divisions of the color scale are not so easily comprehended by many people as the chart which may be conceived in extended landscape. The sky, inasmuch as it spreads itself over the earth and reflects its light upon it, dictates the _tone_ of the scene. The surface of the lake reveals this fact beyond dispute, for the water takes on any tone which the sky may have. The sky’s power of reflection is no less potent in the landscape.
Reflection is observable in that degree in which the surface, reflected upon, is rough or smooth. The absorbent surface allows the light to fall in and disappear and under this condition we see the true or local color. Note, for example, the effect of light on velvet or the hide of a cow in winter. When the hair points toward the light the mass is rich and dark, but when it turns away in any direction its polished surface reflects light, which like the lake becomes a mirror to it.
Light falling upon a meadow will influence it by its own color only in those places where the grass is turned at an angle from its rays.
From these few observations it becomes obvious that unity of tone is a simple matter when understood by the painter and that unity, being a most important part of his color scheme, may be increased by additions of objects bearing the desirable color which nature fails to supply in any particular subject. Thus if the day be one in which a warm mellow haze pervades the air, those tones of the sky repeated upon the backs of cattle, a roadway, clothing, or what not, may effect a more positive tonality than the lesser items would give which also reflect it. Herein then is the principle of Tonality: That all parts of the picture should be bound together by the dominating color or colors of the picture.
With the indoor subject the consideration is equally strong. Let the scheme be one as coloresque as the Venetian school took delight in, vivid primaries in close juxtaposition (see small reproduction in _Fundamental forms—The Cross_). The central figure, that of St. Peter is clothed in dark blue with a yellow mantle. The Virgin’s dress is deep red, her mantle a blue, lighter than that of Peter’s robe. Through the pillars is seen the blue sky of still lighter degree. Thus the sky enters the picture by graded approaches and focalizes upon the central figure. In like manner do the light yellow clouds repeat their color in the side of the building, in the yellow spot in the flag and the mantle of the central figure. The red of the Virgin’s robe and the yellow mantle together form a combination of a yellow red in the flag, the blue and red of the central figures become purple and garnet in the surplices of the kneeling churchmen and doges. The repetition of a given color in different parts of the figure is pushed still further in the blue gray hair of the kneeling figures, the red brown tunics of the monks and the yellow bands upon the draperies.