CAREFUL observation and study of objects in nature, as well as those contrived by man, will reveal one fact of the greatest value to the student of drawing, and this is that although not a little of the beauty of such objects depends on color, on profile and on the proportions of the various parts into which they are divided, more of it than we usually suppose is caused by the varying light and shade and especially by the gradation of tones from light to dark or from dark to light.
There are, to be sure, some objects which seem to have no gradation of tone, each surface being apparently of one value throughout, but in spite of such exceptions there are far more "graded" tones in nature than "flat" tones of uniform appearance, and it is certainly true that a graded tone has more interest and variety than one of exactly the same value in every part.
It naturally follows that in representing nature by drawings, graded tones usually prove of greater value to the artist than do those which are flat. Almost any object can be represented satisfactorily by graded tones, whereas many objects, especially those which are rounded or curved, cannot be made to appear correct if flat tones alone are used. We can, for example, make a pleasing drawing of a square box, and, if we wish, have every tone graded. It is impossible, on the other hand, to nicely represent a sphere or an object of spherical form by the use of flat tones only, unless we resort to a succession of small adjacent flat tones, each slightly different in value from its neighbor, and such a combination really is, after all, a graded tone. If we try to portray a sphere by drawing its outline as at "1," Figure 27, we fail to give our picture any effect of convexity, of form, and shading the entire circle with a flat tone as at "2" gives no better result. It is only when we copy as well as we can the gradations found on such surfaces in nature, as we have done at "3," that we approach the desired effect. In fact we would not even recognize a sphere when placed before us were it not for this subtle grading of its surface tones, for without these gradations it would appear simply as a flat circular disk. In the case of the cylinder and cone and similar rounded forms it is perhaps a bit less difficult to suggest their shapes on paper without recourse to graded tones providing they are drawn in perspective, for when so drawn their forms can be fairly well indicated even in outline. If a real feeling of solidity and roundness is desired, however, it can best be obtained by the use of graded tones. If such objects are shown in elevation, instead of perspective, it will be found that these tones are absolutely essential for their successful representation. Take for example the cylinder which is shown in elevation at "4," Figure 27, drawn in outline only. In this form it appears as a rectangle and seems flat. A smooth tone added as at "5" is of no help, and it is only when we use the grades as at "6" that we get the real appearance of roundness.
Now just as the surfaces of cylinders and spheres and such geometric forms depend largely on gradation of tone for a pleasing effect, so, in architecture too, much of the beauty of the mouldings and ornament depends on similar gradations. After all, the mouldings are mainly combinations of curved surfaces, and if these curves are pleasingly designed the light and dark will be graded in a satisfactory manner. In fact these gradations on mouldings so nicely express the profiles which cause them that we are often able to judge the curve of each moulding at a glance even though its profile is not visible. If the light is favorable we are usually able to name every member composing a cornice and tell its exact form without once seeing its true profile. One of the main reasons why a designer works so hard to produce a good profile for a cornice or similar group of mouldings is that he is seeking the most pleasing arrangement of light and shade and shadow possible, and knows that an excellent profile is important, not as a thing in itself, for it is seen in its true form only at the corners or breaks in a building, but as a means of obtaining the most satisfactory results in light and shade. A poor profile usually means a poor cornice.
At "7," "8," "9" and "10." Figure 27, are four sketches of typical architectural mouldings, drawn in elevation, and with their tones graded. For convenience their profiles have been shown but even if these had been omitted it would not be difficult to visualize the correct curves. It should be borne in mind, however, that without the use of graded tones it would be impossible to produce such effects of curvature.
Now just as it is necessary to use graded tones for a truthful expression of the curved surfaces of mouldings, they are obviously needed also in the representation of other rounded surfaces such as those which we so often find in ornamental work. Most ornament, in fact, consists so largely of curved surfaces of every possible shape that it would be very difficult to represent it on paper without the use of some graded tones. At "11," Figure 27, is a drawing of a rosette, nearly every surface of which is curved, and therefore represented by grades of light and dark. Certainly an object of such gradual curvature as this can be successfully portrayed only by equally subtle gradations of its values.