Architectural terracotta
Architectural terracotta refers to a fired mixture of clay and water that can be used in a non-structural, semi-structural, or structural capacity on the exterior or interior of a building. Terracotta is an ancient building material that translates from Latin as "baked earth". Some architectural terracotta is stronger than stoneware. It can be unglazed, painted, slip glazed, or glazed.
Usually solid in earlier uses, in most cases from the 19th century onwards each piece of terracotta is composed of a hollow clay web enclosing a void space or cell. The cell can be installed in compression with mortar or hung with metal anchors; such cells are often partially backfilled with mortar.
Terracotta can be used together with brick, for ornamental areas; if the source of the clay is the same they can be made to harmonize, or if different to contrast. It is often a cladding over a different structural material.
History
Terracotta was made by the ancient Greeks, Babylonians, ancient Egyptians, Romans, Chinese, and the Indus River Valley and Native American cultures. It was used for roof tiles, medallions, statues, capitals and other small architectural details.Ancient Eastern terracotta
Indian terracotta manufacturers hand pressed, poured, and double-molded the clay mix. Plaster casts have been found in several ancient sites in Afghanistan, Bangladesh, India and Pakistan. Similarities in motifs and manufacturing processes have caused scholars to note cross cultural pollination between the Hellenic and Indus River Valley sculptural terracotta traditions. Famous early examples include the Bhitargaon temple and the Jain temple in the Mahbubnagar district.Chinese, Korean, and Japanese terracotta making traditions were focused on non-architectural uses such as statuary or cookware but various forms of terracotta tiles were popular roofing materials.
Western terracotta
Antiquity–1700s
Greeks used terracotta for capitals, friezes, and other elements of their temples like at Olympia or Selenius. Domestically they used it for statuary and roof tiles. The Etruscans used terracotta for roof tiles, encased beams, and enclosed brick walls with it. The Roman terracotta innovation was the underfloor or hypocaust heating system that they used for their bath houses. Medieval European architecture did not expand terracotta use beyond the ancients. The manufacture of tile roofs diminished with low cost thatch roofing widely available. Southern German, Italian and Spanish city states kept the tradition alive.Image:Natural History Museum London Jan 2006.jpg|thumb|left|upright=1.2|The Natural History Museum in London has an ornate terracotta facade typical of high Victorian architecture – the carvings represent the contents of the museum.
1700s–1880s
Great Britain
Richard Holt and Thomas Ripley patented an artificial stone recipe in 1722. The business was fairly successful at making small architectural ornaments. Their company was taken over by George and Eleanor Coade in 1769. George died a year later, leaving the company to his wife and daughter, both named Eleanor Coade. The Coade ladies popularized the grey mix of terracotta as an alternative to stone with the help of architects like Horace Walpole and Sir John Soane. Georgian architectural style was in vogue and demand for repetitive, classically inspired décor was very fashionable. The Victoria and Albert Museum and the Natural History Museum of London buildings ushered in an era of mass-produced architectural terracotta.North America
Early manufacture: 1840s–1860s
The earliest manufacturer of architectural terracotta in the United States was started by Henry Tolman Jr. in Worcester, Massachusetts, around 1849. In the 1850s, New York City architects like Richard Upjohn and James Renwick used it on some of their projects, but the material failed to gain widespread popularity and many American architects falsely believed it couldn't endure the North American climate.1870s–1930s
The Chicago Fire of 1871 destroyed many of the wood and stone-constructed buildings of Chicago, Illinois, and spurred greater interest in fireproof building materials that could enable the elaborate construction of the era. James Taylor, an English-trained ceramicist, played a key role in establishing effective widespread terracotta production in the United States through his work for various firms such as the Chicago Terra Cotta Company, the Boston Terra Cotta Company, and the New York Architectural Terra-Cotta Company.The American architectural terracotta industry peaked during the late 1800s and helped enable the construction of skyscrapers by allowing for more lightweight construction on top of tall metal-framed structures. The fire-resistance of terracotta protected structural steel on many buildings constructed during this period, such as New York City's Flatiron Building.
There was an increase in popularity of architectural terracotta made with colored, or polychrome, glazed architectural terracotta during the first decade of the 1900s. Architects began to employ combinations of colors to achieve dynamic designs and appearances. This usage diminished as time went on, especially after the success of Cass Gilbert's Woolworth Building increased demand for monochromatic terracotta. Trends in the 1920s favored setbacks in skyscraper towers, leading to increasing demand for sculpted forms in low relief.
1930s–1980s
Usage of terracotta in architecture had diminished through the end of the 1920s and the onset of the Great Depression further harmed the industry: the number of terracotta companies dropped from eighteen in 1929 to eleven in 1933. This was largely attributed to architect's increasing preference for building with cheaper metal, glass, and cement.The time-intensive process of terracotta manufacture put it at a disadvantage compared to newer products. Changing fashions towards more minimalist, modern styles such as the Bauhaus School and International Style further harmed the industry, despite attempts by manufacturers to create products suited to these styles.
Structural problems of earlier terracotta resulting from incomplete waterproofing, improper installation, poor maintenance, and interior corroding mild steel provided bad publicity for terracotta and further harmed its reputation for architects. For much of the 20th century the American terracotta industry was a fraction of its earlier scale and the few surviving companies largely subsisted on jobs producing less complex products like machine-produced ceramic veneers.
Detailed architectural terracotta remained in use through the 1950s and 1960s, however it was often overlooked or misidentified. Architects during this time period did not embrace terracotta's natural properties and instead tended to use it to imitate other materials.
1980s–present
Terracotta experienced a growth in popularity beginning in the 1980s when a resurgence in interest in historic preservation led to demand for architectural terracotta for restoration purposes. Historic manufacturers of terracotta such as Gladding, McBean, Ludowici-Celadon, and newer companies such as Boston Valley Terra Cotta all manufactured pieces used in the restoration of landmarks.Architects became interested in newer uses for terracotta and companies developed products such as rainscreen and wall cladding to allow for dynamic installations that retained terracotta's unique and distinct qualities while working with modern architectural styles.
Manufacturing process
Terracotta can be made by pouring or pressing the mix into a plaster or sandstone mold, clay can be hand carved, or mix can be extruded into a mold using specialized machines. Clay shrinks as it dries from water loss therefore all molds are made slightly larger than the required dimensions. After the desired green-ware, or air dried, shape is created it is fired in a kiln for several days where it shrinks even further. The hot clay is slowly cooled then hand finished. The ceramics are shipped to the project site where they are installed by local contractors. The hollow pieces are partially backfilled with mortar then placed into the wall, suspended from metal anchors, or hung on metal shelf angles.Design
Academically trained artists were often the designers of the terracotta forms. Their drawings would be interpreted by the manufacturer who would plan out the joint locations and anchoring system. Once finalized, the drawings were turned into a plaster reality by sculptors who would create the mold for the craftsmen.File:12-INCH VERTICAL PUG MILL, MANUFACTURED BY THE CROSSLEY MANUFACTURING CO. OF TRENTON, NJ. IT WAS PURCHASED IN 1902, AND USED AT THE FIRST MORAVIAN POTTERY AND TILE WORKS BEFORE HAER PA,9-DOYLT.V,8-28.tif|Vertical pugmill used by the Moravian Pottery and Tile Works in Pennsylvania to refine the clay used for tile production|thumb
Clay preparation
Clay selection was very important to manufacture of terracotta. Homogenous, finer grain sizes were preferred. The color of the clay body was determined by the types of deposits that were locally available to the manufacture. Sand was added to temper the process. Crushed ceramic scraps called grog were also added to stiffen the product and help reduce shrinkage.Weathering the clay allowed pyrites to chemically change to hydrated ferric oxide and reduced alkali content. This aging minimizes the potential chemical changes during the rest of the manufacturing process. The weathered raw clay was dried, ground, and screened. Later, it would have been pugged in a mill that would mix the clay with water using rotating blades and force the blend through a sieve.