A study of John Torreano’s Drawing by Seeing, publ. Harry n. Abrams, inc., NYC, 2007 (ISBN 978-0-8109-9170-5), This is chapter 2: Line constancy.
Because making a line is the first response we have to drawing, the first lesson is to learn to maintain line constancy. The intention is to avoid any variation in intensity—light & dark—within the line itself. You will become less object-oriented and more drawing-oriented.
Use soft pencils, an eraser and a 45cm x 60cm (18”x24) drawing paper. For your subjects, choose simple objects that are self-contained and without a lot of texture or details, such as a cup, a hat, a banana, or an apple. You want to readily see the edges of the whole shape. Make a series of drawings of these simple objects, maintaining control of the line’s intensity for each drawing. Draw one object on each piece of paper, and try to make the image of the object as large as possible and still fit on the page. Because of the increased scale, you will have to make pressure judgments by looking at areas other than the contact point of your pencil. Also, it forces you to anticipate the image’s shape before you draw it, similar to ‘picturing the shot’ before you toss the ball into the basket.
Then try the visual depth cues: the visual devices that give a drawing the illusion of 3-dimensional depth.
1. Position: draw, with line only, the same object in two different positions on the page. Draw one near the top and the other near the bottom. Maintain line constancy and make both drawings the same size. This is a simple exploration of positioning. As such, it is not a strong depth cue. However, having the ability to locate a shape where you want it is crucial. Though the images are the same size, the bottom one will appear closer to the viewer.
2. Size: As before, draw an object twice in the same piece of paper, but this time, vary the size of the drawings. First make a very large one, then a very small one. This is an exercise in size differentiation. Differences in the size of shapes give the illusion of depth, and the largest shape will appear to be closest to the viewer. In customary perception, that which is closer appears visually larger because closer images are larger on the retina.
3. Draw an object in two different positions on the page and make both drawings the same size. This time, however, vary the intensity of the line from one drawing to the next while still maintaining line constancy within each version. Make the first very intense by pressing down hard with your pencil. Then make a very light version. This is an exercise in brightness variation. The most intensely drawn—and therefore seemingly ‘brightest’—shape will appear to be closest to the viewer. This is because, in customary perception, we see things that are closer to us in greater detail than things in the distance.
4. Overlap: When you draw the two objects this time, have them overlap each other. You can vary their sizes, if you like, and be inventive with location, but continue to maintain line constancy throughout the drawing. This drawing is an exercise in making and defining overlaps. In this case, the shape that is ‘in front’ of the others—the one that overlaps most—will appear closest to the viewer, even if it happens to be smaller than the others. Overlap is the most powerful of the four primary depth cues.