We tend to make some assumptions about what drawings are- some are valid, but some may be misleading.
We tend to assume that drawings are linear. Indeed, many are, since implements such as charcoal, pencil, pen, and brush all form lines when drawn across the page. However, many drawings have no explicit lines at all, but rather are created by building up solid areas of value to create masses of light and dark.
We also may assume that drawings are simple and quick, sketches that can be executed in a few minutes, or at most in a few hours. Some artists, for example, Ben Shahn and Picasso are well known for their ability to capture the essence of their subject with only a few strokes. While this is frequently the case, many fine drawings may take far longer to complete.
Because we think drawings are simple and quick, we may also think they are insignificant and inexpensive. Some drawings are insignificant, and may only be a study for a more ambitious project. However, some drawings can be as priceless as any painting. This is particularly true for early drawings, such as Leonardo da Vinci's drawing "The Virgin and Child with St. Anne." This beautifully detailed drawing, also quite large in size (56" x 41")is also valued because fewer complete drawings than paintings survive from this early date.
It is also often assumed that drawings are always in black and white; of course, many colors can be used. Many artists over the centuries have mixed materials, using pen, crayon, chalk, pencil, and ink washes applied with a brush, all in various combinations. Pencils and chalks may be used in any color. One traditional method was to use red chalk on tan paper, with white and black used to create highlights and shadows. This can be seen in Holbein's drawings, as well as many other works of the 15th-19th centuries. Many modern artists may also use the full range of colors in pencils or conte crayon (a type of chalk)-- or other materials. David Hockney's drawings are an example of this technique.
However, there are some characteristics of drawing that make it particularly attractive to the artist in many situations. First, drawing materials are very portable. Therefore it is possible to bring these materials out of the studio, to the subject, or to the workplace or the client, wherever the artist wishes to use his ability to make images.
Also, since the materials are so portable- at a minimum, a sketch pad and a pencil or pen- drawings tend to have a kind of immediacy, and an intimate quality that cannot often be seen in painting or printmaking. It is possible to capture the candid moment, the action, or the mood, without the obtrusive paraphernalia required for other methods. When used in this way, the drawing may also be a more economical way to capture an idea that may simply remain a drawing, or may later be developed in the studio in another medium.