Whereas this method served—within the general stylistic intentions of the 17th century—primarily to elucidate spatial and corporeal proportions, the artists of the 18th century employed it to probe this situation visually with the aid of light. The unmarked area, the spot left empty, has as much representational meaning as the pen contours, the lighter or darker brush accent, and the tinted area.
The art of omission plays a still greater role, if possible, in the later 19th century and in the 20th. Paul Cézanne’s late sheets, with their sparse use of the pencil and the carefully measured out colour nuances, may be considered the epitome of this technique. As the colouring becomes increasingly varied through the use of watercolours to supplement a pen or metalpoint drawing, one leaves the concept of drawing in the strict sense of the term. According to the quality and quantity of the mediums employed, one then speaks of “drawings with watercolour,” “watercolourized drawings,” and “watercolours on preliminary drawings.” The predominant stroke character, rather than the fact that paper is the carrier, is the chief feature when deciding whether or not the work may legitimately be called a drawing.
The combination of dry and fluid drawing mediums provides a genuine surface contrast that may be exploited for sensuous differentiation. Here again a distinction must be made between various ways of applying the identical medium—for example, charcoal and charcoal dust in a water solution or, more frequently, sanguine and sanguine rubbed in with a wet brush—and the stronger contrast brought about by the use of altogether different mediums. Chalk drawings are frequently washed with bistre or watercolour, after the principle of the washed pen drawing. Stronger contrasts, however, can be obtained if the differing techniques are employed graphically, as the Flemish draftsmen of the 17th century liked to do. The Chinese ink wash of chalk drawings also contributes to the illusion of spatial depth. Along with such Dutch painters as Jan van Goyen and members of the family van de Velde, Claude Lorrain achieved great mastery in this technique. The differentiated treatment of the foreground with pen and brush and the background with chalk renders spatial depth plausible and plastic. In modern art, the use of different mediums—whether for plastic differentiation, such as Henry Moore carried out with unequalled mastery in his “Shelter Drawings,” or only for the purpose of contrasting varied surface stimuli of nonrepresentational compositions as well as the enrichment with colours and even with collage elements (the addition of paper, metal, or other actual objects) broadens the concept of the drawing so that it becomes an autonomous picture the mixed technique of which transcends the borderline between drawing and painting. Mechanical devices
Mechanical aids are far less important for art drawing than for any other art form. Many draftsmen reject them altogether as unartistic and inimical to the creative aspect of drawing.
Apart from the crucial importance that mechanical aids have had and continue to have for all kinds of construction diagrams, plans, and other applied drawings, some mechanical aids have been used in varying but significant measure for artistic drawings. The ruler, triangle, and compass as basic geometric instruments have played a major role, especially in periods in which artists created in a consciously constructionist and perspectivist manner. Marks for perspective constructions may be seen in many drawings of early and High Renaissance vintage.
For perspectively correct rendition, the graticulate frame, marked off in squares to facilitate proportionate enlargement or reduction, allowed the object to be drawn to be viewed in line with a screen on the drawing surface. Fixed points can be marked with relative ease on the resultant system of coordinates. For portrait drawings, the glass board used into the 19th century had contours and important interior reference points marked on it with grease crayons or soap sticks, so that they could be transferred onto paper by tracing or direct copying. Both processes are frequently used for preliminary sketches for engravings to be duplicated, as is the screened transmission of a preliminary sketch onto the engraving plate or, magnifying, the painting surface. In such cases the screen lies over the preparatory drawing.
Mirrors and mirror arrangements with reducing convex mirrors or concave lenses were likewise used (especially in the 17th and 18th centuries) as drawing aids in the preparation of reproductions. Even when it was a matter of the most exact rendition of topographical views, such apparatus, as well as the camera obscura (a darkened enclosure having an aperture usually provided with a lens through which light from external objects enters to form an image on the opposite surface), were frequently employed. In a darkened room the desired section is reflected through a lens onto a slanting mirror and from that inverse image is reflected again onto the horizontally positioned drawing surface. Lateral correction can be obtained by means of a second mirror.
Unless the proportions do not allow it, true-to-scale reducing or enlarging can also be carried out with the aid of the tracing instrument called the pantograph. When copying, the crayon or pencil inserted in the unequally long feet of the device reproduces the desired contours on the selected scale.
Most of these aids were thus used in normal studio practice and for the preparation of certain applied drawings. Equally practical, but useful only for closely circumscribed tasks, were elliptic compasses, curved rulers, and stencils, particularly for ornamental and decorative purposes. Only a few present-day artists, notably Jasper Johns, use stencils or simple blocks with a given shape in larger scale composition, in order to obtain the effect of repetition, often in an arbitrary use, in “alienating” technique and colour.
Mechanically produced drawings—such as typewriter sketches, computer drawings, oscillograms—and drawings done with the use of a projector, all of which can bring forth unusual and attractive results, nevertheless do not belong to the topic because they lack the immediate creativity of the art drawing. Applied drawings
Applied and technical drawings differ in principle from art drawings in that they record unequivocally an objective set of facts and on the whole disregard aesthetic considerations. The contrast to the art drawing is sharpest in the case of technical project drawings, the purpose of which is to convey not so much visual plausibility as to give exact information that makes possible the realization of an idea. Such plans for buildings, machines, and technical systems are not instantly readable because of the orthogonal (independent) projection, the division into separate planes of projection, and the use of symbols. Prepared as a rule with such technical aids as ruler and compass, they represent a specialized language of their own, which must be learned. For topographic (detailed delineation of the features of a place) and cartographic (map-making) drawings, too, a special terminology has developed that above all systematizes spatial representations, making them intelligible to the expert with the aid of emblems and symbols.