Which is a short way of saying you can draw hair that is easily believable but the technique may suggest more detail than is actually present.  There are a number of "levels" at which you can tackle your drawing — you might, for example....

• Choose to concentrate on the three-dimensional underlying form.
• Partially overlay the solid shading of form with a resemblance of hair and texture.
• Use the hair itself and its lighting to define the underlying form.

Any level is as valid as any other but my personal preference is for the last of these, as it most resembles reality.

The illustration (above left) shows the use of global shading - treating the subject as a single three-dimensional object without surface texture and applying an overall scheme of tonal values.  In giving visual priority to the underlying form, the presence of hair is left almost entirely to the viewers imagination.

In drawing the Basset (above right) I have used local shading - calculating the light reflection of each hair, or lock of hairs, as it is drawn and applying the required tones.  No global shading exists but all local shading is adjusted with reference to its position within the whole subject.  In this case priority has been given to the outward appearance - three-dimensional form is described only by the hair, its texture and surface highlighting.

If everything "black" was really black and everything "white" was pure white we would see nothing except flat, featureless shapes with sharp outlines. But nothing in life is so simple - in reality reflections and absorbance of light play a full part in what we see. It's the highlights and shadows of a Black Labrador's glossy coat that tell us what shape the dog is - the underlying structure is never overtly seen. The hair, only the hair, defines its three-dimensional form. The same is true of a white Poodle except that the emphasis is reversed - the shadows play a greater part than the highlights. But there is also one other aspect that is as true for each in the drawing process......

Drawing hair is about positive and negative drawing (see introduction to negative drawing) and each has to be understood in its own right before you can effortlessly combine the two and reproduce hair with a sense of reality.

As I stated above, we see black hairs because of their highlights; white hairs are outlined by their shadows.  In both cases the hairs are visible because of their "negative" properties.  In practice you create not the hair but the shadow or highlight.  For black hair the highlight will range from bright, white through a series of darkening greys but not, however, to black - the darkest tones available must be reserved for the positive shadows that define the edges of black hairs not for hairs themselves.

This is the key to negative drawing; the technique that you must learn - as you work, focus your full attention not on the actual lines you are drawing but on the spaces in between them.  In common with watercolour painting, the only white available to the Graphite Artist is the white of the paper.  To produce a white line you must therefore define that line by outlining it in a darker tone.  The line you are drawing has no importance in itself.  It is the space between the lines that is paramount.

Working one small area at a time will make your overall project far easier to handle both mentally and physically and will keep you firmly in control. Don't be tempted to work on the whole drawing at once and nor should you attempt to fill whole areas with tone. Well, Yes - I know your drawing will look more complete far more quickly... and you may feel that it's helping you establish form but beware - the bright highlights you may later wish to create will no longer be achievable, resulting in a distinct loss of life and tonal depth.

Decide on the light direction, consider the position of every hair you define and then apply the illumination accordingly. Defining your hairs and then calculating and adding specific local tone will give them an enhanced reality — don't use global toning and hope it will work locally.