Here’s a quick primer about shading, and the way to create a sense of depth to make your drawings look more “three dimensional.” This is going to be pretty basic and simple, so you’ll be able to start using it immediately.
But first, what is this image a picture of?
Is it a figure? A woman? A statue? The girl who invented cheese?
It’s a picture of a piece of paper with light and dark chalk rubbed on it! That’s all it really is, however, that chalk has been put on the paper in a particular, precise pattern so that your eye recognizes that pattern as a human figure. But it’s still a piece of paper, just like your drawings. Now, the pattern in which the chalk was put down on the paper was done in a very precise way, so precise that it can encode very specific structural details that a viewer’s mind can instantly understand to represent a figure when they look at it. If you look at the drawing closely, you can see how expertly the artist has captured on paper the texture, form, hair, musculature under the skin, shadows, etc. (This drawing is by Pierre-Paul Prud'hon, possibly one of the greatest figure-sketch artists of all time, and a favorite of Marie Antionette).
A computer, at its most basic level, processes everything, whether text documents, pictures or video, as a series of 1s and 0s which are called “bits” of information, and this is known as the “binary” numerical system. Similarly, all visual information can be broken down into 2 bits of information: light and shadow (use of color puts an added spin on the art, but when you understand light and dark first, color becomes much easier and more meaningful to work with).
Most of the time, if you’re drawing, you’re going to be using white or light-colored paper, and the substance you’re going to be drawing with, whether pencil, pen or crayon, is going to be darker.
A “contour drawing” is a line drawing where the line follows the contours, which is to say the edges and details, of the subject of the drawing.
Contour drawings can be great, and convey a lot of detail, but they can also look a little bit flat, since they only convey detail about the edges of what you’re drawing and not about the depth.
Now, when your eye perceives a three dimensional object, what it actually sees is the light reflecting off of that object and into your eye. Because the object is three dimensional, some parts of that object are closer to you than others, and are likely to reflect more light, and the parts farther away from you are more likely to be in shadow. If you’re only using absolute light and dark then the parts of a thing closer to you would be white, and the parts farther away would be black. Like this:
It creates a very bold image, doesn’t it? It’s powerful, but also a little bit cold and if it’s very detailed, it can be confusing.
Notice the transition between light and dark is very intense, “all or nothing,” and the edges all seem very sharp, don’t they? By adding a third, transitional value, we can modulate the intensity of the light and shadow, and create softer, rounder transitions.
The middle tone is half dark and half light—50% of each. And each tone represents how far away from you the object is. This is basic “shading.”
Now we have a lot to work with!
Try playing with this for a while in your drawings and see how many ways you can use this. Your darkest tone is going to be the farthest away, lightest tone is closest, and middle tone is in-between. From here it makes sense that you can continue to split the tones for greater detail as you need them.
Going further—styles of drawing
There are a few other ways of suggesting depth by way of light and shadow, the most common are:
Line weight: Darker, heavier line suggests darkness and depth. It’s an effect that’s used a great deal in cartoons and comics and also in some styles of Asian brush art. It’s also sometimes used in technical illustration.
Cross hatching: Etchings, line drawing and pen-and-ink art typically utilize only solid lines. In that case, the half-tone can be approximated by increasing the density of the lines or "cross hatching." By applying more lines in a particular area, it blocks out a certain amount of the light reflecting back to the viewer’s eye, say, 50% of the reflected light, which is the same thing that the 50% (solid grey) half-tone did earlier.
There are many ways to imply shading with line alone: cross hatching, stippling (little dots), and other textures you can make up yourself. Notice that they all suggest different surface textures to the viewer.
Look at all the textures the famous illustrator, Harry Clarke, used in this illustration for Poe's "Tales of Mystery and Imagination."
If you’re just starting out, you can take for granted that the brightest part of the image will be closest to you, in the way we’ve been discussing. But after you begin to get some familiarity with the ins and outs of shading, you’ll begin to notice that sometimes the light may not be closest to you.
Also, be aware that that in different cultures, different rules may apply. In Asian Painting, for example, closer objects are often darker, while distant objects may be lighter, as if disappearing into a fog.
Guptill, Arthur L.-- Rendering in Pen and Ink: The Classic Book on Pen and Ink Techniques for Artists, Illustrators, Architects, and Designers
Eisner, Will-- Graphic Storytelling and Visual Narrative
Simmons, Gary-- The Technical Pen
Now go and have fun with this stuff!
(c) 2010 Jeff Sauber
Harry Clarke illustration from http://www.grandmasgraphics.com/index.php