Clay is the most common material used for modeling. Fine-grained minerals like earthenware, stoneware and porcelain are suitable for sculpture. Clay slabs or coils can be created to build your sculpture or apply several layers of clay. You can apply the first layer of clay and allow the piece to harden before applying more clay. Apply as many layers of clay as you need to finish your piece. Air-dry clay can be used for modeling, eliminating the need for a firing; however, the finished product is not water-resistant and is more fragile. Modeling may be combined with carving and the finished piece can be fired according to the requirements of the material used.
Plaster is an inexpensive material that doesn't require firing, but the figure is not as resistant as clay. Plaster of Paris is most commonly used and this is added to water to obtain a paste, which can be applied on the frame using your hands or a palette knife. It's essential that the plaster is not too liquefied so you can work with it. Apply several levels of plaster, allowing each level to dry before proceeding. Imperfections can be corrected before the plaster dries or you can use sandpaper to make changes to your sculpture.
Papier mache, or papier-mâché, is a technique you can use in sculpture. You mix white glue with the same amount of water and cut some newspaper strips. Color pigments can be used in the glue solution to obtain a colored sculpture. Each paper strip is soaked in the diluted glue solution and applied on your wire armature. Allow the paper to dry and apply several layers of paper until you obtain a sturdy sculpture. Afterward, you can sand the sculpture and paint it.
Wax may be used both for modeling and mold-casting sculptures. Microcrystalline wax is most commonly used and you can obtain an extremely smooth surface, which is very malleable. This technique is recommended for more experienced sculptors. You melt the wax using a double boiler and add colors to the mixture, because it is more difficult to color the wax after it is dry. The wax doesn't have to be hot when you start working, but it should be malleable. Apply small amounts of wax on your armature and allow it to dry. If you need to make changes, use a heated blade to sculpt your piece.