Like all work which is planned for a purpose, a sgraffito design begins with a preliminary sketch, which is gradually worked up into a working drawing. The technical demands of the medium dictate the first translation of the purely artistic idea into a suitable style.
Besides using very definite lines and surfaces of uniform color, the shapes in the composition must be suitable for execution with a stylus and cutting spatula. Austere and angular drawing without much detail is the most effective, whether the work is done in the classical black and white or uses several colors.
The cutting technique of sgraffito is best approached by making a cartoon from the first sketch, not with pencil or brush, but by building up the design from cut-out shapes of colored paper. This procedure is very useful for every kind of graphic decoration and will be dealt with more fully when we draft our batik design.
It is difficult to work out a well-balanced composition without fitting the sketched idea as soon as possible into a scale drawing of the whole facade. The scale may be chosen, according to the size of the proposed work, between 1 :20, 1: 10 and 1 :5. The larger the proportion, the easier it will be to transfer the design to full size.
If several colors are used, it should be borne in mind that the strictness of the form makes each color much more insistent than in a painting. If a fresco on a facade were to be changed into a sgraffito, or a plaster intarsia, in as many colors, it could be done only by reducing many of the gradations and mergings, or overrunnings of tone, into one distinct color. This color would then stand out independently in its own right. To find a harmonious effect that does not break up the whole unity of the facade requires a thorough study of color problems, particularly as we are further restricted by the fact that many colors are not compatible with lime (see section on Painting).
To begin with, we are confined to a basis of one color, that of the top layer of plaster. In two-color sgraffito (a monochrome would be a colorless plaster-cut) the essential effect is the contrast with the top layer of plaster; in polychrome the combined effect of all the colors forms the contrast with the top coat. By attempting otherwise we risk the possibility of one predominant color destroying the unity of the design, unless the main color be used pervasively and more lineally.
It may be more enjoyable to color the sgraffito plaster oneself than to buy it ready-colored; however, ready-made colored plaster saves trouble and is guaranteed durable. It can be chosen from a color card to a specified granulation and comes ready for the plasterer to add water and apply it. Buying ready-made plaster is considerably cheaper than preparing it oneself because one does not have at hand supplies of the various sands needed to give the plaster its basic color.
It is easy to make a stronger color by adding a small amount of pigment, but good pigments are expensive and it takes a large amount to color white plaster. Pigment also works like earth in the plaster and in large quantities reduces the binding effect of lime and cement. Furthermore, a lot of drying tests will be needed, since damp plaster is always much darker and more strongly colored than dry.
Sgraffito coats are always applied so that the darkest layer is lowest and the brightest color is on top. Over it all comes the finishing coat that covers the whole building. It is tempting to apply very thick layers in order to obtain as plastic an effect as possible with strong shadow outlines. This may look well at first, but the process soon becomes tedious, quite apart from the fact that deep cutting endangers the permanency of the work and destroys the formal unity of the design. In the long run a sgraffito worked in thin coats is more effective and professional looking than one which
looks like an applique of fretwork.