How to Make Terra Cotta

A terra cotta sculpture

Terra cotta is one of the oldest building materials and sculpting media. The term simply means "baked earth" in Latin. Used in ancient times to make pipes, cooking pots, bricks, cornices and architectural ornaments, its principal use today is in the sculpture and tile that bear its unmistakable orangish color and porous texture.

Difficulty:

Moderately Easy

Instructions

Things You'll Need

• Clay Water Glaze (optional) Kiln Tongs

1. Mix clay. Terra cotta--as opposed to earthenware, which is mostly soil--is simply a mixture of fine-grained clays made of primarily silica, alumina, and other alkaline material such as lime. Ready powdered mixes can be purchased that, when mixed with water, yield a malleable clay. Recycled clay that hasn't been fired is called "grog" and can be used like new terra cotta.

2. Shape. Wet or partially dried terra cotta can be molded by hand, on a pottery wheel or using a cast.

3. Apply glaze (optional). Unlike some forms of pottery, terra cotta is not glazed after it has been fired. Therefore, if the finish product is going to be waterproofed, a glaze containing variable proportions of water and metallic oxides can be sprayed on the piece to produce either a matte, satin or gloss finish. Powders in the gloss can also be added to modify the color of the finished product.

4. Dry and fire. After allowing the terra cotta mix to dry and harden somewhat, it is fired in a pottery kiln at a temperature of 1,080 degrees Celsius, which is hotter than a bisque firing. Firing can take from as little as 3 to as many 20 hours depending on the moisture of the clay and the thickness of the design. Use tongs to handle or remove hot clay from the kiln.

Tips & Warnings

• The major advantages of terra cotta are that it is inexpensive and quick to produce. Substituting terra cotta for more expensive materials can significantly reduce the overall cost of a project.

• Unglazed terra cotta is very porous and tends to absorb moisture from its surroundings. This can result in cracking during frosts.

Resources

• Read this Article in Spanish
• Video: How to Make Terracotta Sculptures
• Friends of Terra Cotta
• Video: Terracotta Firing vs. Bisque Firing
• Terra Cotta
• Firing Clay