Collect references, such as photos or drawings of a head, to use while chiseling. You can also have a friend or family member model for you.
Set up a mold for pouring a plaster block by clamping together four boards to make a box. Make the box big enough to accommodate the size of the head. Set the box on a larger base board. Use either plastic-coated boards or coat the boards with oil soap to ensure easy release of the plaster. Seal all the seams on the outside of the box with wet clay.
Mix your plaster by slowly scooping handfuls of plaster into a bucket of water. Get rid of any clumps by crumbling them with your fingers. Keep adding plaster until a small hill of plaster rises from the surface of the water. Let the plaster sit for a few minutes while it incorporates the water and becomes a consistent, smooth mixture.
Give the plaster a couple of stirs with a wooden stick and scrape the bottom of the bucket. Pour the plaster into your box. Tamp the sides of the box gently with a rubber mallet to dissipate any bubbles. Let the plaster sit until it sets and dries. Depending on the ambient humidity and the size of your box, your plaster block should set in approximately 20 minutes.
Remove the boards to reveal the block of plaster.
Loosely sketch where the features will go on the block with a permanent marker.
Chisel the head. Many tools can be used for carving plaster. Masonry tools, wood carving tools, clay tools and dental tools all work great. Use a chisel and hammer to start breaking off large areas of plaster. Carve smaller areas of plaster with a clay loop tool. Use a wood rasp or grater for quick sanding. Use clay and dental needle tools for obtaining fine details, like around the eyes and mouth, or to show strands of hair. Sand down smooth surfaces with wet sandpaper.
Keep referring to your reference materials as you work. Obtain accurate proportion by making comparative measurements. Make a comparative measurement by comparing the length of one feature of the face to another feature of the face in your reference, and then follow those measurements when carving. For example, you might look at the length of the lips in your reference and then assess that the forehead is double the length of the lips.
Dust off your head when finished. Leave the head white, paint it with oil paint or finish it with varnish or lacquer.