There are three principal methods or systems of giving relief by adding to our outline.
One is the method of giving relief to form by contrasts of tone, colour, or tint.
Another by means of the expression of light and shade: and the third by means of modelling in relief.
Now, still keeping to expression by means of line, the three arms I have sketched (p. [167]) illustrate: (1) the form in outline alone; (2) the contrast method; and (3) the light and shade method. The three pots underneath illustrate the same three stages in a simpler manner.
In number one we see the outline defining the form pure and simple: in number two the form is relieved by a half-tone formed of diagonal lines, forming a plane or background behind it. The arm is still further relieved by the dark drapery. Number three shows the relief carried further by lines expressive of the modelling of the arm and the rounding of the pot, and also by cast shadows from the forms.
The system of expressing relief I have termed relief by contrast includes two kinds of contrast: there are the contrasts of line and form, and there are the contrasts of planes of tone or tint and local colour. We may consider that the contrast method covers generally all forms of pattern and certain kinds of pictorial design. The method of expressing relief by means of line covers generally all forms of design in black and white, graphic sketching, pen-drawing, and work with the point of all kinds.
Of the Use of Contrast and Planes
Taking the principle of contrast as applied to pattern design, we can, even within the limited range of black and white and half-tint (as expressed by lines), get a considerable amount of decorative effect. In the first place by bringing out our pattern, previously outlined, upon a black ground (as in Nos. 1 and 2, p. [169]), increasing the richness of effect, and getting a second plane by treating the lower part in an open tint of line.