Terra cotta (Italian: "baked earth") is a ceramic. Its uses include vessels, water & waste water pipes and surface embellishment in building construction. The term is also used to refer to items made out of this material and to its natural, brownish orange color.
Production and properties
An appropriate refined clay ("grog
") is partially dried and cast, molded, or hand worked into the desired shape. After further thorough drying it is placed in a kiln, or atop combustible material in a pit, and then fired. After pit firing the hot ware is covered with sand to cool, and after kiln firing the kiln is slowly cooled. When unglazed, the material will not be waterproof, but it is suitable for in-ground use to carry pressurized water (an archaic use), for garden ware, and sculpture or building decoration in tropical environments, and for oil containers, oil lamps, or ovens. Most other uses such as for table ware, sanitary piping, or building decoration in freezing environments require that the material be glazed. Terra cotta, if uncracked, will ring if lightly struck, but not as brightly as will ware fired at higher temperature, which is called stoneware
. The fired material is relatively weak compared to stoneware.
Some types of terra cotta are created from grog made from recycled terra cotta.
The unglazed color after firing can vary widely, but most common clays contain enough iron to cause an orange, orangish red, or brownish orange color, with this range including various colors described as "terra cotta". Other colors include yellow, gray, and pink.
Terra cotta has been used throughout history for sculpture
, as well as bricks
and roof shingles
. In ancient times, the first clay sculptures were dried (baked) in the sun after being formed. Later, they were placed in the ashes of open hearths to harden, and finally kilns
were used, similar to those used for pottery today. However only after firing to high temperature would it be classed as a ceramic material. The most famous terra cotta statues are those of the Terracotta Warriors
Significant uses of terra cotta have included Emperor Qin Shi Huang
's Terracotta Army
of China, built in 210
. Mass producers of mold-cast and fired terra cotta figurines were also the ancient Greeks of Tanagra
. French sculptor Albert-Ernest Carrier-Belleuse
made many terra cotta pieces, but possibly the most famous is The Abduction of Hippodameia
depicting the Greek mythological scene of a centaur kidnapping Hippodameia on her wedding day. American architect Louis Sullivan
is well-known for his elaborate glazed terra cotta
ornamentation, designs that would have been impossible to execute in any other medium. Terra cotta and tile were used extensively in the town buildings of Victorian Birmingham
Precolonial West African sculpture also made extensive use of terra cotta. The regions most recognized for producing terra cotta art in this part of the world include the Nok culture of central and north-central Nigeria, the Ife/Benin cultural axis in western and southern Nigeria (also noted for its exceptionally naturalistic sculpture), and the Igbo culture area of eastern Nigeria, which excelled in terra cotta pottery. These related, but separate, traditions also gave birth to elaborate schools of bronze and brass sculpture in the area.
Crude terra-cotta female figurines were uncovered by archaeologists in excavations of Mohenjo-daro and Harappa, the two large urban sites that tell about the Indus Valley period (3000-1500 B.C.E.) in Hindu history. Along with phallus-shaped stones, these suggest some sort of fertility cult and a belief in a Mother Goddess.
In chemistry, pieces of terra cotta are used as a heterogeneous catalyst to "crack" long-chain alkanes. This process is useful for obtaining more useful products, such as gasoline or petrol, from less useful ones, such as highly viscous long chain alkanes.
Advantages in sculpture
As compared to bronze sculpture
, terra cotta uses a far simpler process for creating the finished work with much lower material costs. Reusable mold-making techniques may be used for series production. Compared to marble sculpture
and other stonework the finished product is far lighter and may be further glazed to produce objects with color or durable simulations of metal patina. Robust durable works for outdoor use require greater thickness and so will be heavier, with more care needed in the drying of the unfinished piece to prevent cracking as the material shrinks. Structural considerations are similar to those required for stone sculpture.