The creation of any part of the human form in art is one of the most sought-after skills, as well as one of the most challenging. The creation of a human face leaves little margin for error, as even the smallest mistakes are easy to recognize for most viewers. When sculpting the human face, either in clay or in relief, success comes through a careful study of proportion and positioning as well as an understanding of the particulars of this area of anatomy.
Observing the Face
The greatest challenges in sculpting the human face come from the temptation to sculpt what one expects the structures of the face to be rather than what they actually are. Spend some time looking at your face and those of others around you, as well as touching and discerning the shapes and structures (this is especially helpful for sculpture as it gives you a tactile sense of shape, positioning and proportion).
If you can get a hold of a model of a human skull, or at least some photos from several angles, observe this shape as well. The human face is far from a flat plane and is informed by the facial structure of the skull. Notice especially the shape of the eye sockets and protruding areas of bone, such as cheekbones and nasal bone, and the shape of the jaw and teeth. The face with flesh does not have as many drastic changes of shape as the skull, but the changes it does have are a reflection of these proportions and depths.
Sculpting the Features
After a rough oval shape of the facial plane is set up for sculpting, it is time to realize the features. One common temptation that must be avoided is the tendency to place the eyes too high on the face. Visually, we perceive the eyes to be the top of the face, but they are really located just above the vertical center line. Positioning the eyebrows before any other features is therefore a good way to start, both because eyebrows are a relatively easy shape to master on the first try and because they're a good way to gauge the positioning of the other features.
When setting up the eyes, pay attention to symmetry: if your eyes aren't placed at an equal height, equally sized and placed at equal distanced from the vertical center line of the face, you may not notice a problem until you start to sculpt the nose and other features (at which point the face will start to look quite wrong).
Remember that the eyeballs themselves are more or less spherical shapes that are wrapped in the flesh of the eyelids; while this gives the visible portion of the eye a lemon shape in two-dimensional art, a flat, lemon-shaped eye in a sculpture is a mistake. Speaking of eyelids, sculpt both the top and the bottom lid. With fully opened eyes, both lids tend to cover about an equal portion of the eyeball, though the top lid is larger and thus, more folded.
The nose is a shape that is easy to underestimate. It is more drastic in its shape than you might think. The very top of the nasal bone starts as a curved indentation (this is easy to miss) but then slopes down and out to protrude further from the face than any other features. In clay sculpting, it's best to add a new piece of clay for the nose and blend it, rather than pulling out from the rest of the clay; with relief sculpture, be sure to set the rest of the face back from the tip of the nose to leave yourself enough room. In most cases, the tip of the nose should be straight and the nostrils of equal size and symmetrical shape, unless your subject has a markedly crooked nose.
When sculpting the mouth, it's important to realize that the slight protrusion of the lips is a gradual slope out that starts from the bottom of the nose at the top and from just above the chin at the bottom. It can be tempting to simply carve or affix a pair of shaped lips in the form of the colored part of the mouth, but this will look cartoonish and unrealistic.
Most people have some protrusion of both the chin and cheekbones, though it will be more or less true for different individuals and different ethnicities. As with the nose, add extra clay for these and blend or leave material for carving in relief sculpture.
