Architectural Terra Cotta

Vol. XXII No. 1 - SPRING 2011

By: Kathy Gemperle

Architectural Terra Cotta refers to a high grade of aged clay that has been mixed with sand and pulverized fired clay for use on buildings. The word comes from the Latin, “cooked earth” which refers to the heating of the clay to temperatures in the range of 2000-2350 degrees Fahrenheit. The terra cotta was used to enhance the decorative aspects of architecture and it became popular in the 1870s in the United States after a decade of use in England. Clay as a building material had the advantage of being both inexpensive, light weight and easily molded into a variety of shapes

The process of creating a decorative piece to be attached to the exterior of the building was essentially a handmade process. Molds were designed in decorative styles such as Classical Revival, Beaux Arts and Baroque with curling spirals and leaf designs. These molds were made from clay prototypes by hand. In the 1920s the designs were influenced by the discovery of King Tut’s tomb and the Egyptian influence flourished. Architects could choose from catalogs of available styles or create designs for a custom project like the former bank building at the northwest corner of Clark and Balmoral or the now lost terra cotta griffins on the building at 5715 Clark Street (the former Scientific Cleaners). A change in terra cotta in the 1920s included the use of tiles on the entire façade of some buildings such as the one at 5256 N. Clark (SW corner of Berwyn and Clark).

Placing multiple pieces of glazed terracotta on a building involved first choosing the mold designs and including them in the architectural drawings. The pieces chosen had to be made oversized in order to allow for shrinkage. Once the clay was pressed into the plaster mold, it was removed and glazed. The glaze is a coating of silica, clay and minerals mixed in water which when fired leaves a smooth and hardened surface. The most popular color was white or beige. Brighter colors might be golds, greens and blues or accents of orange. Each piece had to be carefully numbered to insure installation in the correct position. The whole process took eight weeks from the time of ordering. The mold pieces were rather thin compared to the bricks and stone used in buildings. These thin pieces had to be applied to concrete when being attached to the building. The use of glaze on these pieces began in the 1890s. By the 1920s, terra cotta was in use as accents on many brick buildings.

There were several companies that produced terra cotta for buildings in the Chicago area. The Northwest Terra Cotta Company had its works at Wrightwood and Clybourn from 1877 to 1956.

The American Terra Cotta company began in 1883 in a town then called Terra Cotta, Illinois, now known as Crystal Lake. It operated as a clay company until 1966. Louis Sullivan produced designs for this company for the 12 years that he worked there. Another company, the Midland Terra Cotta Company began in Chicago in 1910 and was absorbed into the American Terra Cotta Company in 1938.

The downturn in production came in the 1930s when, because of the Depression, most building ceased. Also, the 1930s brought the influence of the modern simplicity, and few architects wanted elaborate details on the exterior of their buildings. Now in 2011, the issue is the preservation of the terra cotta on many historical buildings.

While terra cotta itself is essentially waterproof like your coffee mug or toilet it is installed in blocks or pieces and sometimes care was not taken in the attachment of the terra cotta to the building or to the other pieces with grout. Because of the freeze and thaw cycle in many cities, the terracotta can actually take on water, expand and cause the glaze to crack called crazing. Then the protection of the glaze surface is diminished and the freeze and thaw process can lead to more serious cracking and something called spalling, where pieces of the glaze and clay fall off the building.

Today there are a few companies that specialize in this restoration. New materials have been developed and new methods of anchoring loose pieces. The process is complex. Should you want to learn more, I suggest two web sites. Boston Valley Terra Cotta in Orchard Park, New York, has a web site filled with photos. This is the company that was used to recreate the main level “new” terra cotta for the Belle Shore restoration by architect Thom Greene. The National Park Service has an extensive article on the preservation of architectural terra cotta. Just search Architectural Terra Cotta. Also of interest is the National Building Museum in Washington, D.C.