About Clay

History of Clay

Clay is native earth containing clay minerals and very little organic material. It is found along the banks of rivers and streams where they flow down off mountains. Ancient people living in river valleys used clay to make containers for mixing and storing food. Terra cotta, the Latin words for baked earth, usually brownish red in color, is the common name for most clays used for shaping and firing. Until clay is baked, or fired, it can be crushed and reformed into other shapes. Once it is fired in a very hot oven or kiln, the chemical structure is changed, so it retains its shape. The oldest known pottery was made in Japan about 12,000 years ago. Ancient cultures in China, Egypt, Greece, and Mesopotamia, as well as Native Americans, also fired clay pottery. Most cultures decorated clay vessels with incised or painted patterns and glazes.

Techniques

Modeling (pinch–pull)

To form a basic shape (for animals and figures, use a pear shape), pinch and pull out some areas of the clay and push in others. Press the side of a stick into the shape, making a cross, to mark the location of the legs and arms. Keep the form compact, but for even drying and firing, make sure the thickest section is less than an inch across.

Slabs and Plaques

On a smooth, dry surface covered with plastic sheeting or heavy cloth, roll a lump of clay into a slab, using a rolling pin or dowel and guides about 1/4” thick. Keep the thickness uniform. Place a template or pattern on top and cut around it.

Coil Building

Form worms of clay by pinching or rolling lumps of clay into long, even shapes. Attach the coils to a slab base, one on top of another, building layers of rings, attaching each with scoring and slip.

Construction

Attach clay pieces together by first scoring a rough surface into both pieces where they will be joined, then adding a thin layer of slip and pressing the pieces together.

Etching

Etch designs in the clay before it dries using such tools as craft picks, pencils, nails, or plastic knives. Fine carving can be done on leather-hard clay.

Glazing

Clay objects must be dried and usually bisque fired before glazing. Brush glaze on using a soft, wide brush, applying several coats.

Finishing Clay Projects

Preparing Clay for Firing

Make sure clay pieces are no thicker than about 1”. If necessary, use a knife or wire tool to hollow out the center of the object.

Drying

Let clay dry slowly in a temperate room, to prevent cracking. Cover clay with damp towels, so the outside dries at the same rate as the inside. Let clay dry for a minimum of 2–3 weeks. It will feel cool to the touch when dry.

Firing

Fire clay at high temperatures in a kiln, to permanently harden it. Follow kiln instructions for correct cone size. A second firing is necessary only if ceramic glazes are going to be used.

To Add Color (choose one):

1. Paint with ceramic underglazes, then refire. Apply colored glazes in thin coats. Leave some areas natural. Wait a few minutes for each coat to dry before adding the next coat. One coat of color will appear translucent after firing, while each additional coat will make the color more opaque. Keep the glaze in the glaze containers clean. Don’t mix colors. Avoid dipping brushes directly into the glaze container by distributing glaze on saucers or foam palettes.
2. Paint the fired clay using tempera paint or watercolor.

To Add a Glossy Finish (choose one):

1. Paint the fired clay with clear ceramic glaze. Apply one or two coats of glaze, leaving some areas unglazed for contrast. Use a damp sponge to clean off excess clear glaze from the bottom of the clay pieces so glaze doesn’t stick to the kiln. Refire.
2. Spray the fired clay with an acrylic glaze and let it dry. (Recommended: Krylon Spray)
3. Using tongs or wearing gloves, dip the fired sculpture into a wide-mouth container filled with liquid floor wax. For a shinier finish, dip twice, letting it dry a few minutes between dips.

Maintenance of Materials

Clay Storage

Store bricks of clay in plastic bag to prevent drying out. Place a damp cloth over clay to resist drying or add water to reconstitute dry clay. Store at room temperature.

Glaze Reconstitution

Dried out glazes can be reconstituted by adding a little water to them. Stir with a fork until consistency is that of thick cream.